How to remove c0hen Locker ransomware from the operating system
Written by Tomas Meskauskas on (updated)
What is c0hen Locker?
Discovered by cyber security researcher Jack, c0hen Locker is a malicious program classified as ransomware. Malware within this classification is designed to encrypt the data of infected devices and then demand ransom payments from the victims (i.e., payment for decryption tools/software).
When the encryption is underway, all files are renamed with the ".c0hen" extension. For example, a filename such as "1.jpg" would appear as "1.jpg.c0hen", and so on. Once this process is complete, c0hen Locker displays a pop-up window that contains the ransom message.
The message within the pop-up informs victims that all devices within their network have been infected with c0hen Locker ransomware. I.e., all systems in the network have been affected and associated data has been encrypted. The message claims that the only way to restore data is to follow the instructions of the cyber criminals behind the infection.
Victims must pay the ransom of 0.15 BTC (approximately equivalent to 1100 USD). The address of the criminals' Bitcoin cryptowallet address is also provided. The message instructs users to download the Discord application and contact the c0hen Locker developers through an email address provided.
This window has a field to enter the decryption/unlock key, thereby initiating the decryption process. While, in most cases of ransomware infections, decryption is impossible without the involvement of the individuals responsible, c0hen Locker's encryption can be decrypted.
The unlock key (12309482354ab2308597u235fnq30045f) has been provided by Jack, the malware researcher credited with discovery of this ransomware. It is likely that in future releases of c0hen Locker and updated variants, this flaw will be addressed.
Therefore, the unlock key will no longer work. Regardless, you are strongly advised against meeting the ransom demands of cyber criminals. Despite paying, victims receive none of the necessary keys/tools to decrypt their files. Their data thus remains encrypted and useless, and they experience significant financial loss.
Since manual decryption is not possible, the only viable solution is to recover data from a backup, if one was made before the infection and was stored in a different location. To prevent ransomware from further encryption, it must be eliminated from the operating system. Unfortunately, removal will not restore already compromised files.
Screenshot of a message encouraging users to pay a ransom to decrypt their compromised data:
NEMTY 2.5 REVENGE, Zeoticus, Back, and BDDY are some examples of other ransomware-type programs. This class of malware is defined by data encryption and ransom demands. Crucial differences between these infections include cryptographic algorithm they use (symmetric or asymmetric) and size of ransom payments.
Ransoms typically range between three and four digit sums (in USD). Cyber criminals tend to prefer digital currencies (primarily, cryptocurrencies), since these transactions are difficult/impossible to trace. To protect files from these infections, keep backups on remote servers and/or unplugged storage devices. It is best to store multiple backups in several different locations.
How did ransomware infect my computer?
Ransomware and other high-risk infections mainly originate from dangerous attachments to emails sent in spam campaigns, trojans, illegal activation ("cracking") tools, fake updaters and untrustworthy download channels. The term "spam campaign" refers to the act of sending deceptive emails on a mass scale.
The messages are usually disguised as "official", "important", "urgent" and so on. Infectious files are attached to (or linked in) these emails, and they can be in various formats (e.g. Microsoft Office and PDF documents, archive and executable files, JavaScript, etc.).
When they are executed, run or otherwise opened. the infection process is initiated (i.e., they begin downloading/installing malware). Trojans are malicious programs possessing capabilities to cause chain infections. Rather than activating licensed products, illegal activation tools ("cracks") can download/install malicious software.
Rogue updaters infect systems by misusing weaknesses of outdated programs and/or installing malware rather than the promised updates.
Untrustworthy download channels such as Peer-to-Peer sharing networks (BitTorrent, Gnutella, eMule, etc.), unofficial and free file-hosting websites, third party downloaders and similar can offer malicious content for download (e.g. presented as normal software and/or bundled with it).
| Name | C0hen Locker virus |
| Threat Type | Ransomware, Crypto Virus, Files locker. |
| Encrypted Files Extension | .c0hen |
| Ransom Demanding Message | Text presented in the pop-up window. |
| Ransom Amount | 0.15 BTC (~1100 USD) |
| Cyber Criminals' Cryptowallet Address | 18Fh68NJrMZCiTqq1VoWaQsSb8pxDjEw6N (Bitcoin) |
| Cyber Criminal Contact | c0hen#7722 (Discord) |
| Detection Names | Avast (Win32:Malware-gen), BitDefender (Gen:Heur.Ransom.RTH.1), ESET-NOD32 (A Variant Of MSIL/Filecoder.WB), Kaspersky (HEUR:Trojan-Ransom.MSIL.Gen.gen), 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. |
| Additional Information | C0hen Locker is decryptable ransomware. The unlock key is 12309482354ab2308597u235fnq30045f provided by cyber security researcher, Jack. |
| 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
Be cautious when opening emails and attached files, or links within them. Suspicious and/or irrelevant mail should not be opened, especially if received from unknown senders (addresses). All attachments (and links) found in suspect messages must never be opened, as these files are the potential source of infection.
Use only official and verified download channels. Use functions/tools provided by genuine developers to activate and update programs. Software "cracking" (illegal activation) tools and third party updaters should be avoided, since they carry a high risk of malware installation.
It is paramount to device safety to have a reputable anti-virus/anti-spyware suite installed and kept up-to-date. Furthermore, this software should be used to perform regular system scans and for the removal of detected threats.
If your computer is already infected with c0hen Locker, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate this ransomware.
Text presented in c0hen Locker ransomware pop-up window:
c0hen@admin
WARNING: if you turn your PC off you will not get your files back!!!
c0hen locker has infected your PCWhats happening? All devices on your network have been infected All of your computer files have been encrypted with ransomware
Your computer has been infected. You must do as instructed to get your files back.
Donate 0.15 BTC to this wallet BTC wallet: 18Fh68NJrMZCiTqq1VoWaQsSb8pxDjEw6N
Or:
Download discord and add c0hen#7722 for decryption key
discord.com/download
Screenshot of files encrypted by c0hen Locker (".c0hen" extension):
c0hen Locker 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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By downloading any software listed on this website you agree to our Privacy Policy and Terms of Use. To use full-featured product, you have to purchase a license for Combo Cleaner. 7 days free trial available. Combo Cleaner is owned and operated by Rcs Lt, the parent company of PCRisk.com read more.
Video suggesting what steps should be taken in case of a ransomware infection:
Quick menu:
- What is C0hen Locker 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.
Outstanding!
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