Elimination instructions for Gusau ransomware
Written by Tomas Meskauskas on (updated)
What is Gusau?
Gusau is high-risk ransomware that belongs to a family of viruses called Djvu. Following successful infiltration, Gusau encrypts most stored data rendering it unusable. Additionally, Gusau appends names of all encrypted files with the ".gusau" extension (hence the ransomware name).
For example, "sample.jpg" is renamed to "sample.jpg.gusau". Additionally Gusau generates a text file named "_readme.txt" and stores it on the desktop. As with most ransomware from the Djvu family, Gusau was first discovered by malware security researcher, Michael Gillespie.
Most ransomware infections deliver an identical ransom-demand message, and Gusau is no exception. The message informs victims of the current situation and states that files can only be restored with a unique decryption key - unfortunately, this information is accurate.
Gusau encrypts data using an algorithm that generates a unique decryption key individually for each victim. Decrypting files without this key is impossible. Cyber criminals store all keys on a remote server and blackmail victims for their release. To receive a decryption key and restore files, each victim must pay a ransom of $980.
To receive payment/decryption instructions, victims are encouraged to contact cyber criminals via an email address provided or telegram. The message also states that victims who contact criminals within 72 hours after encryption will receive a 50% discount (the cost will drop to $490).
Additionally, victims are permitted to send one selected file to Gusau's developers, which is then restored and returned as a 'guarantee' that they are capable of restoring files and can be trusted. Be aware, however, that many ransomware developers ignore victims once payments are submitted.
Therefore, paying usually gives no positive result and victims are scammed. For these reasons, ignore all requests to contact these people or submit payments.
Gusau encrypts files with a so-called "offline key" whenever the server is not responding or the infected machine has no Internet connection. Therefore, try to restore files with this decrypter developed by Michael Gillespie. The only other possible solution is to restore everything from a backup.
Screenshot of a message encouraging users to pay a ransom to decrypt their compromised data:
There are hundreds of ransomware-type infections, all of which are virtually identical (e.g., 1BTC, V6cye, and foSTE). As with Gusau, most of these infections encrypt data so that developers can blackmail victims by offering paid recovery of files. There are typically just two major differences: 1) size of ransom, and; 2) type of encryption algorithm used.
Unfortunately, encryptions are typically performed using cryptographies such as RSA, AES, and similar that generate unique decryption keys. Therefore, unless the virus is not fully developed or has bugs/flaws, restoring data manually (without the involvement of developers) is impossible.
Gusau and other similar viruses present a strong case for maintaining regular backups, however, store them on a remote server (e.g., Cloud) or unplugged storage device (external hard drive, Flash drive or similar). This will prevent ransomware from encrypting backups together with regular data.
Note that there is always a chance that servers and hardware can be damaged. Therefore, we strongly advise you to have multiple backup copies stored in different locations.
How did ransomware infect my computer?
Infections such as Gusau are usually distributed using fake software updaters and 'cracks', trojans, third party software download sources, and spam email campaigns. Fake updaters and cracks work in an identical way. They inject malware rather than updating/activating software.
Trojans cause chain infections. They stealthily infiltrate computers and download/install additional malware. Unofficial download sources such as free file hosting/freeware download websites, Peer-to-Peer [P2P] networks (torrents, eMule, etc.) and similar, are used to proliferate malware by presenting it as legitimate software.
In this way, users are tricked into downloading and installing malware. Finally, spam email campaigns are used to send hundreds of thousands of deceptive emails that contain malicious attachments and deceptive messages encouraging recipients to open them.
The attachments are often presented as 'important documents' (bills, receipts, invoices, or similar) in attempts to give the impression of legitimacy and increase the chance of tricking recipients.
| Name | Gusau virus |
| Threat Type | Ransomware, Crypto Virus, Files locker |
| Detection Names | BitDefender (Trojan.Worm.GenericKDS.41479463), Emsisoft (Trojan.Worm.GenericKDS.41479463 (B)), ESET-NOD32 (A Variant Of Win32/Kryptik.GUSY), McAfee (Artemis!80D04BE9495D), Full List (VirusTotal) |
| Encrypted Files Extension | .gusau |
| Ransom Demanding Message | _readme.txt |
| Ransom Amount | $980/$490 |
| Cyber Criminal Contact | gorentos@bitmessage.ch, verasto@firemail.cc, @datarestore (Telegram) |
| 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 | This malware is designed to show fake a Windows Update window, modify the Windows "hosts" file (to prevent users from accessing cyber security websites) and inject AZORult trojan into the system. |
| 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?
The main reasons for computer infections are poor knowledge of these threats and careless behavior. The key to computer safety is caution. Therefore, pay close attention when browsing the Internet and downloading, installing, and updating software. Never open email attachments that are irrelevant or when the sender seems suspicious/unrecognizable.
Download your programs from official sources only, preferably using direct download links. The same applies to software updates. Installed applications/operating systems should be updated using implemented functions or tools provided by the official developer.
Third party downloaders/installers/updaters often include rogue applications and, therefore, do not use them. Be aware that software piracy is a cyber crime (cracking installed applications is illegal) and the risk of infection is extremely high, since many cracks are fake.
Therefore, never attempt to activate software using illegal/third party tools. Have a reputable anti-virus/anti-spyware suite installed and running.
This will significantly diminish the chance of infection, since software of this type detects and eliminates most infections before the system is damaged. The key to computer safety is caution. If your computer is already infected with Gusau, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate this ransomware.
Text presented in Gusau ransomware text file ("_readme.txt"):
ATTENTION!
Don't worry, you can return all your files!
All your files like photos, databases, documents and other important are encrypted with strongest encryption and unique key.
The only method of recovering files is to purchase decrypt tool and unique key for you.
This software will decrypt all your encrypted files.
What guarantees you have?
You can send one of your encrypted file from your PC and we decrypt it for free.
But we can decrypt only 1 file for free. File must not contain valuable information.
You can get and look video overview decrypt tool:
hxxps://we.tl/t-g2wRDh3Pih
Price of private key and decrypt software is $980.
Discount 50% available if you contact us first 72 hours, that's price for you is $490.
Please note that you'll never restore your data without payment.
Check your e-mail "Spam" or "Junk" folder if you don't get answer more than 6 hours.
To get this software you need write on our e-mail:
gorentos@bitmessage.ch
Reserve e-mail address to contact us:
varasto@firemail.cc
Our Telegram account:
@datarestore
Mark Data Restore
Your personal ID:
-
Screenshot of files encrypted by Gusau (".gusau" extension):
Malware researcher Michael Gillespie has developed a decryption tool that might restore your data if it was encrypted using an "offline key". As mentioned, each victim gets a unique decryption key, all of which are stored on remote servers controlled by cyber criminals.
These are categorized as "online keys", however, there are cases whereby the infected machine has no Internet connection or the server is timing out/not responding. If this is the case, Gusau will use an "offline encryption key", which is hard-coded. Cyber criminals change offline keys periodically to prevent multiple encryptions with the same key.
Michael Gillespie continually gathers offline keys and updates the decrypter, however, the chances of successful decryption are still very low, since only a very small proportion of "offline keys" have so far been gathered.
You can download the decrypter by clicking this link (note that the download link remains identical, even though the decrypter is being continually updated). Your files will be restored only if the list of gathered keys includes the one that was used to encrypt your data.
Screenshot of STOP/Djvu decrypter by Michael Gillespie:
As with most ransomware from the Djvu family, Gusau also displays a fake Windows update pop-up during the encryption:
IMPORTANT NOTE! - As well as encrypting data, ransomware-type infections from the Djvu malware family also install a trojan-type virus called AZORult, which is designed to steal various account credentials. Moreover, this malware family is designed to add a number of entries to the Windows hosts file.
The entries contain URLs of various websites, most of which are related to malware removal. This is done to prevent users from accessing malware security websites and seeking help. Our website (PCrisk.com) is also on the list.
Removing these entries, however, is simple - you can find detailed instructions in this article (note that, although the steps are shown in the Windows 10 environment, the process is virtually identical on all versions of the Microsoft Windows operating system).
Screenshot of websites added to Windows hosts file:
Gusau 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 Gusau 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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