Interlock (.interlock) ransomware virus – removal and decryption options
Written by Tomas Meskauskas on (updated)
What kind of malware is Interlock?
Interlock is a ransomware that encrypts files and demands payment for the decryption. In addition to a Windows variant, there is a version of Interlock targeting Linux operating systems.
When we executed a sample of this ransomware on our test machine, it encrypted files and added a ".interlock" extension to their filenames. For example, a file originally named "1.jpg" appeared as "1.jpg.interlock", "2.png" as "2.png.interlock", etc. Afterward, Interlock dropped a ransom note titled "!__README__!.txt". Double extortion is also used to force victims into paying.
Interlock ransomware targets large entities and has been used in attacks leveraged against US governmental organizations and companies operating within the healthcare and technology spheres. Additionally, the malware was used to target manufacturing companies in Europe. However, Interlock attacks appear opportunistic and not exclusive to these sectors.
Screenshot of files encrypted by Interlock ransomware:
Ransom note overview
Interlock ransomware's message informs the victim that their organization network has been breached. Important files were encrypted, and sensitive data was exfiltrated (e.g., backups, business-critical files, contracts, legal and financial documents, personal data, client information, etc.).
The victim is given 96 hours to contact the attackers. By complying with the cyber criminals' demands, the victim will receive the decryption tools, and the stolen information will be deleted. If they refuse to cooperate, the vulnerable data will be leaked or sold, and media outlets, regulators, and competitors will be alerted of the attack.
Additionally, the victim is warned against modifying the affected files (i.e., renaming, moving, attempting decryption, etc.), as that will render them undecryptable.
Interlock ransomware overview
The functionality of Interlock's Windows and Linux versions is essentially the same. Significant similarities are to be found in how these programs carry out encryptions based on multithreading, check parameters, and self-delete following encryption. Naturally, some of the variation is due to the environment being different operating systems.
The Windows variant is better geared towards anti-detection, as it recovers the executable's original code before executing it (code patching). While the Linux version first checks the execution arguments. Checking arguments is how both operate prior to determining the further course of action.
Encryption arguments are the same in both: either only a specific file is encrypted, or all files in a directory and its subdirectories are. If neither argument is used, then everything is encrypted (barring exceptions): in Windows – from the C drive's top directory; in Linux – from the root directory.
OS differences dictate those in the file and directory exclusion lists; the goal of the malware is to avoid rendering the infected device inoperable or otherwise causing issues.
The Windows version alone utilizes a persistence-ensuring mechanism that involves registering and deleting tasks with Task Scheduler. The way these variants approach self-deletion differs; one significant difference is that the Windows version also eliminates logs from the Event Viewer.
The manner in which the Windows variant operates leaves little room for stopping the attack midway, while the Linux version may be limited. This variant could be blocked from further encryption by restricting the file and folder permissions to the user account. Additionally, an EDR (Endpoint Detection and Response) solution could be able to prevent this version from executing malicious processes or to create a software safelist that only permits pre-approved applications to run.
In most ransomware infections, decryption is impossible without the attackers' interference. The rare exceptions are cases involving deeply flawed ransomware.
However, paying does not guarantee data recovery since cyber criminals often do not send the promised decryption key/software despite receiving the ransom. Therefore, we strongly advise against complying. Remember that sending money to criminals supports their illegal activities.
To prevent Interlock ransomware from further encryptions – it must be eliminated from the network. Unfortunately, removal will not restore already locked files.
The only solution is to recover them from a backup (if one is available). Keep in mind that it is best practice to keep backups in multiple different locations, such as remote servers, unplugged storage devices, and others.
Ransomware examples
Kasper, Weaxor, Nyxe, and Heda are merely a few of our latest articles on ransomware. While this malware operates practically the same throughout (i.e., data encryption for ransom demands), there are two major differences.
These programs can use different cryptographic algorithms (symmetric or asymmetric) to encrypt data. Ransoms can differ significantly (from three to eight digits in USD) depending on the intended victim – home users vs. large entities (e.g., companies, organizations, institutions, etc.).
How did ransomware infect my computer?
In the known Interlock attacks, this ransomware was infiltrated into systems using a RAT (Remote Access Trojan). The trojan was proliferated under the guise of a fake Google Chrome browser update promoted on a legitimate news website that had been hacked.
The RAT did download a genuine Chrome setup, but it also executed embedded PowerShell scripts to download/install a credential-targeting stealer and a keylogger (program for recording keyboard input).
Stolen credentials, RDP (Remote Desktop Protocol) services, and programs like AnyDesk and PuTTY – were used to move between systems. In one of the attacks, the infection and data collection took over two weeks before Interlock was executed and the encryption began.
It must be mentioned that other techniques and infection chains could be used by Interlock. Generally, malware is proliferated using phishing and social engineering tactics. Malicious programs are usually disguised as or bundled with ordinary content.
Infectious files can be executables (.exe, .run, etc.), archives (RAR, ZIP, etc.), documents (Microsoft Office, Microsoft OneNote, PDF, etc.), JavaScript, and so on. Merely opening a virulent file can be enough to trigger the infection.
Malware is primarily distributed via trojans, drive-by (stealthy/deceptive) downloads, online scams, malicious attachments/links in spam mail (e.g., emails, PMs/DMs, SMSes, etc.), malvertising, untrustworthy download channels (e.g., freeware and third-party sites, P2P sharing networks, etc.), illegal software activation tools ("cracks"), and fake updates.
Some malicious programs can even self-spread via local networks and removable storage devices (e.g., external hard drives, USB flash drives, etc.).
| Name | Interlock virus |
| Threat Type | Ransomware, Crypto Virus, Files locker |
| Encrypted Files Extension | .interlock |
| Ransom Demanding Message | !__README__!.txt |
| Free Decryptor Available? | No |
| Cyber Criminal Contact | Website on Tor network |
| Detection Names | Combo Cleaner (Trojan.Generic.36878051), DrWeb (Trojan.Encoder.41165), ESET-NOD32 (A Variant Of Win32/Kryptik.HXUY), Kaspersky (Trojan-Ransom.Win32.Crypmod.ayca), Microsoft (Trojan:HTML/Redirector.PAN!MTB), Full List Of Detections (VirusTotal) |
| Symptoms | Cannot open files stored on your computer, previously functional files now have a different extension (for example, my.docx.locked). A ransom demand message is displayed on your desktop. Cyber criminals demand payment of a ransom (usually in bitcoins) to unlock your files. |
| Distribution methods | Infected email attachments (macros), torrent websites, malicious ads. |
| Damage | All files are encrypted and cannot be opened without paying a ransom. Additional password-stealing trojans and malware infections can be installed together with a ransomware infection. |
| Malware Removal (Windows) | To eliminate possible malware infections, scan your computer with legitimate antivirus software. Our security researchers recommend using Combo Cleaner. |
How to protect yourself from ransomware infections?
We strongly recommend downloading only from official and verified sources. Additionally, all programs must be activated and updated using legitimate functions/tools, as those acquired from third-parties can contain malware.
Another recommendation is to be vigilant when browsing since the Internet is rife with fraudulent and malicious content. We advise approaching incoming emails and other messages with caution. Attachments or links present in suspicious/irrelevant mail must not be opened, as they can be infectious.
It is essential to have a reputable anti-virus installed and kept updated. Security software must be used to run regular system scans and to remove detected threats and issues. If your computer is already infected with Interlock, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate this ransomware.
Appearance of Interlock ransomware's text file "!__README__!.txt" (GIF):
Text presented in this message:
INTERLOCK - CRITICAL SECURITY ALERT
To Whom It May Concern,
Your organization has experienced a serious security breach. Immediate action is required to mitigate further risks. Here are the details:
THE CURRENT SITUATION
- Your systems have been infiltrated by unauthorized entities.
- Key files have been encrypted and are now inaccessible to you.
- Sensitive data has been extracted and is in our possession.
WHAT YOU NEED TO DO NOW
1. Contact us via our secure, anonymous platform listed below.
2. Follow all instructions to recover your encrypted data.
Access Point: -
Use your unique Company ID: -
DO NOT ATTEMPT:
- File alterations: Renaming, moving, or tampering with files will lead to irreversible damage.
- Third-party software: Using any recovery tools will corrupt the encryption keys, making recovery impossible.
- Reboots or shutdowns: System restarts may cause key damage. Proceed at your own risk.
HOW DID THIS HAPPEN?
We identified vulnerabilities within your network and gained access to critical parts of your infrastructure. The following data categories have been extracted and are now at risk:
- Personal records and client information
- Financial statements, contracts, and legal documents
- Internal communications
- Backups and business-critical files
We hold full copies of these files, and their future is in your hands.
YOUR OPTIONS
#1. Ignore This Warning:
- In 96 hours, we will release or sell your sensitive data.
- Media outlets, regulators, and competitors will be notified.
- Your decryption keys will be destroyed, making recovery impossible.
- The financial and reputational damage could be catastrophic.
#2. Cooperate With Us:
- You will receive the only working decryption tool for your files.
- We will guarantee the secure deletion of all exfiltrated data.
- All traces of this incident will be erased from public and private records.
- A full security audit will be provided to prevent future breaches.
FINAL REMINDER
Failure to act promptly will result in:
- Permanent loss of all encrypted data.
- Leakage of confidential information to the public, competitors, and authorities.
- Irreversible financial harm to your organization.
CONTACT US SECURELY
1. Install the TOR browser via hxxps://torproject.org
2. Visit our anonymous contact form at -
3. Use your unique Company ID: -
4. Review a sample of your compromised data for verification.
5. Use a VPN if TOR is restricted in your area.
Screenshot of Interlock's chat website on Tor network:
Video showing how to remove Interlock ransomware using Combo Cleaner:
Interlock ransomware removal:
Instant automatic malware removal:
Manual threat removal might be a lengthy and complicated process that requires advanced IT skills. Combo Cleaner is a professional automatic malware removal tool that is recommended to get rid of malware. Download it by clicking the button below:
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Video suggesting what steps should be taken in case of a ransomware infection:
Quick menu:
- What is Interlock virus?
- STEP 1. Reporting ransomware to authorities.
- STEP 2. Isolating the infected device.
- STEP 3. Identifying the ransomware infection.
- STEP 4. Searching for ransomware decryption tools.
- STEP 5. Restoring files with data recovery tools.
- STEP 6. Creating data backups.
If you are a victim of a ransomware attack we recommend reporting this incident to authorities. By providing information to law enforcement agencies you will help track cybercrime and potentially assist in the prosecution of the attackers. Here's a list of authorities where you should report a ransomware attack. For the complete list of local cybersecurity centers and information on why you should report ransomware attacks, read this article.
List of local authorities where ransomware attacks should be reported (choose one depending on your residence address):
USA - Internet Crime Complaint Centre IC3
United Kingdom - Action Fraud
Spain - Policía Nacional
France - Ministère de l'Intérieur
Germany - Polizei
Italy - Polizia di Stato
The Netherlands - Politie
Poland - Policja
Portugal - Polícia Judiciária
Isolating the infected device:
Some ransomware-type infections are designed to encrypt files within external storage devices, infect them, and even spread throughout the entire local network. For this reason, it is very important to isolate the infected device (computer) as soon as possible.
Step 1: Disconnect from the internet.
The easiest way to disconnect a computer from the internet is to unplug the Ethernet cable from the motherboard, however, some devices are connected via a wireless network and for some users (especially those who are not particularly tech-savvy), disconnecting cables may seem troublesome. Therefore, you can also disconnect the system manually via Control Panel:
Navigate to the "Control Panel", click the search bar in the upper-right corner of the screen, enter "Network and Sharing Center" and select search result: 
Click the "Change adapter settings" option in the upper-left corner of the window: 
Right-click on each connection point and select "Disable". Once disabled, the system will no longer be connected to the internet. To re-enable the connection points, simply right-click again and select "Enable". 
Step 2: Unplug all storage devices.
As mentioned above, ransomware might encrypt data and infiltrate all storage devices that are connected to the computer. For this reason, all external storage devices (flash drives, portable hard drives, etc.) should be disconnected immediately, however, we strongly advise you to eject each device before disconnecting to prevent data corruption:
Navigate to "My Computer", right-click on each connected device, and select "Eject": 
Step 3: Log-out of cloud storage accounts.
Some ransomware-type might be able to hijack software that handles data stored within "the Cloud". Therefore, the data could be corrupted/encrypted. For this reason, you should log-out of all cloud storage accounts within browsers and other related software. You should also consider temporarily uninstalling the cloud-management software until the infection is completely removed.
Identify the ransomware infection:
To properly handle an infection, one must first identify it. Some ransomware infections use ransom-demand messages as an introduction (see the WALDO ransomware text file below).
This, however, is rare. In most cases, ransomware infections deliver more direct messages simply stating that data is encrypted and that victims must pay some sort of ransom. Note that ransomware-type infections typically generate messages with different file names (for example, "_readme.txt", "READ-ME.txt", "DECRYPTION_INSTRUCTIONS.txt", "DECRYPT_FILES.html", etc.). Therefore, using the name of a ransom message may seem like a good way to identify the infection. The problem is that most of these names are generic and some infections use the same names, even though the delivered messages are different and the infections themselves are unrelated. Therefore, using the message filename alone can be ineffective and even lead to permanent data loss (for example, by attempting to decrypt data using tools designed for different ransomware infections, users are likely to end up permanently damaging files and decryption will no longer be possible even with the correct tool).
Another way to identify a ransomware infection is to check the file extension, which is appended to each encrypted file. Ransomware infections are often named by the extensions they append (see files encrypted by Qewe ransomware below).
This method is only effective, however, when the appended extension is unique - many ransomware infections append a generic extension (for example, ".encrypted", ".enc", ".crypted", ".locked", etc.). In these cases, identifying ransomware by its appended extension becomes impossible.
One of the easiest and quickest ways to identify a ransomware infection is to use the ID Ransomware website. This service supports most existing ransomware infections. Victims simply upload a ransom message and/or one encrypted file (we advise you to upload both if possible).
The ransomware will be identified within seconds and you will be provided with various details, such as the name of the malware family to which the infection belongs, whether it is decryptable, and so on.
Example 1 (Qewe [Stop/Djvu] ransomware):
Example 2 (.iso [Phobos] ransomware):
If your data happens to be encrypted by ransomware that is not supported by ID Ransomware, you can always try searching the internet by using certain keywords (for example, a ransom message title, file extension, provided contact emails, crypto wallet addresses, etc.).
Search for ransomware decryption tools:
Encryption algorithms used by most ransomware-type infections are extremely sophisticated and, if the encryption is performed properly, only the developer is capable of restoring data. This is because decryption requires a specific key, which is generated during the encryption. Restoring data without the key is impossible. In most cases, cybercriminals store keys on a remote server, rather than using the infected machine as a host. Dharma (CrySis), Phobos, and other families of high-end ransomware infections are virtually flawless, and thus restoring data encrypted without the developers' involvement is simply impossible. Despite this, there are dozens of ransomware-type infections that are poorly developed and contain a number of flaws (for example, the use of identical encryption/decryption keys for each victim, keys stored locally, etc.). Therefore, always check for available decryption tools for any ransomware that infiltrates your computer.
Finding the correct decryption tool on the internet can be very frustrating. For this reason, we recommend that you use the No More Ransom Project and this is where identifying the ransomware infection is useful. The No More Ransom Project website contains a "Decryption Tools" section with a search bar. Enter the name of the identified ransomware, and all available decryptors (if there are any) will be listed.
Restore files with data recovery tools:
Depending on the situation (quality of ransomware infection, type of encryption algorithm used, etc.), restoring data with certain third-party tools might be possible. Therefore, we advise you to use the Recuva tool developed by CCleaner. This tool supports over a thousand data types (graphics, video, audio, documents, etc.) and it is very intuitive (little knowledge is necessary to recover data). In addition, the recovery feature is completely free.
Step 1: Perform a scan.
Run the Recuva application and follow the wizard. You will be prompted with several windows allowing you to choose what file types to look for, which locations should be scanned, etc. All you need to do is select the options you're looking for and start the scan. We advise you to enable the "Deep Scan" before starting, otherwise, the application's scanning capabilities will be restricted.
Wait for Recuva to complete the scan. The scanning duration depends on the volume of files (both in quantity and size) that you are scanning (for example, several hundred gigabytes could take over an hour to scan). Therefore, be patient during the scanning process. We also advise against modifying or deleting existing files, since this might interfere with the scan. If you add additional data (for example, downloading files/content) while scanning, this will prolong the process:
Step 2: Recover data.
Once the process is complete, select the folders/files you wish to restore and simply click "Recover". Note that some free space on your storage drive is necessary to restore data:
Create data backups:
Proper file management and creating backups is essential for data security. Therefore, always be very careful and think ahead.
Partition management: We recommend that you store your data in multiple partitions and avoid storing important files within the partition that contains the entire operating system. If you fall into a situation whereby you cannot boot the system and are forced to format the disk on which the operating system is installed (in most cases, this is where malware infections hide), you will lose all data stored within that drive. This is the advantage of having multiple partitions: if you have the entire storage device assigned to a single partition, you will be forced to delete everything, however, creating multiple partitions and allocating the data properly allows you to prevent such problems. You can easily format a single partition without affecting the others - therefore, one will be cleaned and the others will remain untouched, and your data will be saved. Managing partitions is quite simple and you can find all the necessary information on Microsoft's documentation web page.
Data backups: One of the most reliable backup methods is to use an external storage device and keep it unplugged. Copy your data to an external hard drive, flash (thumb) drive, SSD, HDD, or any other storage device, unplug it and store it in a dry place away from the sun and extreme temperatures. This method is, however, quite inefficient, since data backups and updates need to be made regularly. You can also use a cloud service or remote server. Here, an internet connection is required and there is always the chance of a security breach, although it's a really rare occasion.
We recommend using Microsoft OneDrive for backing up your files. OneDrive lets you store your personal files and data in the cloud, sync files across computers and mobile devices, allowing you to access and edit your files from all of your Windows devices. OneDrive lets you save, share and preview files, access download history, move, delete, and rename files, as well as create new folders, and much more.
You can back up your most important folders and files on your PC (your Desktop, Documents, and Pictures folders). Some of OneDrive’s more notable features include file versioning, which keeps older versions of files for up to 30 days. OneDrive features a recycling bin in which all of your deleted files are stored for a limited time. Deleted files are not counted as part of the user’s allocation.
The service is built using HTML5 technologies and allows you to upload files up to 300 MB via drag and drop into the web browser or up to 10 GB via the OneDrive desktop application. With OneDrive, you can download entire folders as a single ZIP file with up to 10,000 files, although it can’t exceed 15 GB per single download.
OneDrive comes with 5 GB of free storage out of the box, with an additional 100 GB, 1 TB, and 6 TB storage options available for a subscription-based fee. You can get one of these storage plans by either purchasing additional storage separately or with Office 365 subscription.
Creating a data backup:
The backup process is the same for all file types and folders. Here’s how you can back up your files using Microsoft OneDrive
Step 1: Choose the files/folders you want to backup.
Click the OneDrive cloud icon to open the OneDrive menu. While in this menu, you can customize your file backup settings.
Click Help & Settings and then select Settings from the drop-down menu.
Go to the Backup tab and click Manage backup.
In this menu, you can choose to backup the Desktop and all of the files on it, and Documents and Pictures folders, again, with all of the files in them. Click Start backup.
Now, when you add a file or folder in the Desktop and Documents and Pictures folders, they will be automatically backed up on OneDrive.
To add folders and files, not in the locations shown above, you have to add them manually.
Open File Explorer and navigate to the location of the folder/file you want to backup. Select the item, right-click it, and click Copy.
Then, navigate to OneDrive, right-click anywhere in the window and click Paste. Alternatively, you can just drag and drop a file into OneDrive. OneDrive will automatically create a backup of the folder/file.
All of the files added to the OneDrive folder are backed up in the cloud automatically. The green circle with the checkmark in it indicates that the file is available both locally and on OneDrive and that the file version is the same on both. The blue cloud icon indicates that the file has not been synced and is available only on OneDrive. The sync icon indicates that the file is currently syncing.
To access files only located on OneDrive online, go to the Help & Settings drop-down menu and select View online.
Step 2: Restore corrupted files.
OneDrive makes sure that the files stay in sync, so the version of the file on the computer is the same version on the cloud. However, if ransomware has encrypted your files, you can take advantage of OneDrive’s Version history feature that will allow you to restore the file versions prior to encryption.
Microsoft 365 has a ransomware detection feature that notifies you when your OneDrive files have been attacked and guide you through the process of restoring your files. It must be noted, however, that if you don’t have a paid Microsoft 365 subscription, you only get one detection and file recovery for free.
If your OneDrive files get deleted, corrupted, or infected by malware, you can restore your entire OneDrive to a previous state. Here’s how you can restore your entire OneDrive:
1. If you're signed in with a personal account, click the Settings cog at the top of the page. Then, click Options and select Restore your OneDrive.
If you're signed in with a work or school account, click the Settings cog at the top of the page. Then, click Restore your OneDrive.
2. On the Restore your OneDrive page, select a date from the drop-down list. Note that if you're restoring your files after automatic ransomware detection, a restore date will be selected for you.
3. After configuring all of the file restoration options, click Restore to undo all the activities you selected.
The best way to avoid damage from ransomware infections is to maintain regular up-to-date backups.
Frequently Asked Questions (FAQ)
How was my computer hacked and how did hackers encrypt my files?
Interlock ransomware has been observed being proliferated via a fake browser update carrying a RAT (Remote Access Trojan). Other distribution methods are possible. Generally, malware is spread through trojans, drive-by downloads, online scams, dubious download sources (e.g., freeware and free file-hosting sites, P2P sharing networks, etc.), fake updaters, illegal program activation tools ("cracks"), spam mail, and malvertising.
How to open ".interlock" files?
Continued file usage necessitates decryption. In other words, encrypted files cannot be opened/used unless they are decrypted.
Where should I look for free decryption tools for Interlock ransomware?
In case of a ransomware attack, we advise looking up the No More Ransom project website (more information above).
I can pay you a lot of money, can you decrypt files for me?
We do not provide decryption services. In fact, recovering ransomware-encrypted files is usually impossible without the attackers' interference. Therefore, third-parties offering paid decryption are often scams or aim to act as middlemen between victims and criminals.
Will Combo Cleaner help me remove Interlock ransomware?
Combo Cleaner will scan your device and eliminate active ransomware infections. It must be stressed that running a full system scan is crucial since sophisticated malicious programs typically hide deep within systems.
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