Remove Mosk ransomware from operating systems

Also Known As: Mosk virus
Distribution: Moderate
Damage level: Severe

Mosk ransomware removal instructions

What is Mosk?

Discovered by Michael Gillespie, Mosk is a malicious program and part of the STOP/Djvu ransomware family. It is designed to encrypt data and keep it inaccessible, until a ransom is paid. When Mosk encrypts data, it renames all files with the ".mosk" extension. Therefore, "1.jpg" becomes "1.jpg.mosk", and so on for all affected files. Once this process is complete, a text file ("_readme.txt") is created and stored on the victim's desktop.

The message in "_readme.txt" states that all of the victim's important data, such as databases, documents, photos and other important files, have been encrypted with the strongest encryption and a unique key. The only way to restore files is to purchase a decryption tool and key (individually generated for each victim) from the cyber criminals behind Mosk. Users are offered free decryption of one file as 'proof' that recovery is possible, however, the test file must not contain important information (likely, implying that it cannot be a database, backup, large excel sheet, or similar). The cost of decryption software/key (ransom) is stated to be $980. If contact is made within 72 hours, this sum is reduced by 50 percent. Two email addresses are listed in the message, via which victims are to contact the criminals. Additionally, users are informed that, should they not receive a response within six hours, they are to check their "Spam/Junk" email folders for the reply. Typically, ransomware encryption cannot be "cracked" with free tools. Therefore, only the individuals who originally encrypted the data are capable of decrypting it. Regardless, cyber criminals cannot be trusted and you are strongly advised against meeting their demands or paying any ransoms. Victims who pay often receive none of the promised decryption tools - their data remains damaged beyond repair and they experience financial loss. While removing Mosk will not restore compromised data, it will prevent this malicious software from further encryption. Encrypted files can be recovered from a backup, provided one was made before the infection and stored separately.

Screenshot of a message encouraging users to pay a ransom to decrypt their compromised data:

Mosk decrypt instructions

GodLockForvDecrypme, and FuxSocy ENCRYPTOR are some examples of malicious programs similar to Mosk. All ransomware operates by encrypting data and demanding payment for decryption. The main differences for this type of malware include the cryptographic algorithm used for encryption and size of ransom. The latter ranges between three-digit and four-digit sums (in USD). Cyber criminals usually demand that these payments are made via digital currencies (e.g. cryptocurrencies, pre-paid vouchers), since these transactions are difficult/impossible to trace. Decryption without the involvement of the criminals behind the ransomware infection is generally impossible, unless the malware is still in development and/or has certain bugs/flaws. To protect data from infections and other damage, keep backups on remote servers and/or unplugged storage devices. Preferably, multiple backup copies should be stored in different locations.

How did ransomware infect my computer?

Ransomware and other malware is spread through trojans, spam campaigns, untrustworthy download channels, fake software updaters and illegal activation tools ("cracks"). Trojans are malicious programs that operate by downloading/installing additional malware. Spam or junk mail campaigns refer to the tactic of sending out deceptive emails on a massive scale. These emails are commonly disguised as "official", "important", "priority" and similar. They contain infectious attachments (or links leading to them), which come in various formats: archive and executable files, Microsoft Office and PDF documents, JavaScript, etc. When these attachments are executed, run or otherwise opened, they begin downloading/installing malicious software. Unofficial and free file-hosting websites, P2P sharing networks (BitTorrent, eMule, Gnutella, etc.) and other third party downloaders are classed as untrustworthy. These download sources can present malicious content as legitimate products or normal programs bundled with malware. Fake software updaters and illegal activation ("cracking") tools infect systems in a similar manner, primarily by downloading/installing malware, rather than updating software or activating licensed products.

Threat Summary:
Name Mosk virus
Threat Type Ransomware, Crypto Virus, Files locker.
Encrypted Files Extension .mosk
Ransom Demanding Message _readme.txt
Ransom Amount $980/$490
Cyber Criminal Contact and
Detection Names AVG (FileRepMalware), BitDefender (Trojan.GenericKD.32686342), ESET-NOD32 (A Variant Of Win32/Kryptik.GYAA), DrWeb (Trojan.Encoder.3953), Full List Of Detections (VirusTotal)
Rogue Process Name 5.exe or TBVGRFCED.EXE
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 a fake Windows Update window and modify the Windows "hosts" file to prevent users from accessing cyber security websites (more information below).
Distribution methods Infected email attachments (macros), torrent websites, malicious ads, unofficial activation and updating tools.
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.

To eliminate Mosk virus our malware researchers recommend scanning your computer with Spyhunter.
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How to protect yourself from ransomware infections

Do not open or read suspicious, irrelevant emails, despite any deceptive 'priority' labels they might have. Do not open attachments or links within these emails, since this is the origin of potential system infections. Use official and verified download channels, as opposed to various sharing networks and other third party downloaders. Software should be activated via legitimate means. Note that using illegal activation tools ("cracks") is high-risk. The same extends to program updating, which should be performed with tools/functions provided by genuine developers. Third party updaters are often bogus and install malware rather than the promised updates. You are strongly advised to have a reputable anti-virus/anti-spyware suite installed and kept up-to-date. This software can be used for regular system scans and removal of detected threats/issues. If your computer is already infected with Mosk, we recommend running a scan with Spyhunter for Windows to automatically eliminate this ransomware.

Text presented in Mosk ransomware text file ("_readme.txt"):


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:
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:

Reserve e-mail address to contact us:

Your personal ID:

Screenshot of files encrypted by Mosk (".mosk" extension):

Files encrypted by Mosk

Screenshot of fake Windows update pop-up displayed during the encryption:

Fake Windows pop-up displayed by Mosk during the encryption

Screenshots of Mosk ransomware process variants in Task Manager:

Mosk ransomware process variant 1 Mosk ransomware process variant 2

IMPORTANT NOTE! - As well as encrypting data, ransomware-type infections from the Djvu malware family also 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 ( 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:

Tro Ransomware adding websites to Windows Hosts file

There are currently two versions of Djvu ransomware infections: old and new. The old versions were designed to encrypt data by using a hard-coded "offline key" whenever the infected machine had no internet connection or the server was timing out/not responding. Therefore, some victims were able to decrypt data using a tool developed by cyber security researcher, Michael Gillespie, however, since the encryption mechanism has been slightly changed (hence the new version, released in August, 2019), the decrypter no longer works and it is no longer supported. If your data has been encrypted by an older version, you might be able to restore it with the another tool developed by Emsisoft and Michael Gillespie. It supports a total of 148 Djvu variants and you can find more information, as well as download link and decryption instructions on Emsisoft's official web page.

Screenshot of Djvu decryption tool by Emsisoft and Michael Gillespie:

Djvu ransomware decrypter by Michael Gillespie and Emsisoft

Additionally, Emsisoft is now providing a service that allows to decrypt data (again, only if it was encrypted by Djvu variants released before August, 2019) for those victims who have a copy of the file before and after encryption. Victims simply upload the pair of original and encrypted file to Emsisoft's Djvu decryption web page and download the aforementioned decryption tool (the download link will be provided after uploading files). Note that file processing may take some time, so be patient. Note that the system must have an internet connection during the entire decryption process, otherwise it will fail.

Screenshot of Emsisoft Djvu decryption service web page:

Djvu ransomware decryption service by Emsisoft

Mosk ransomware removal:

Instant automatic removal of Mosk virus: Manual threat removal might be a lengthy and complicated process that requires advanced computer skills. Spyhunter is a professional automatic malware removal tool that is recommended to get rid of Mosk virus. Download it by clicking the button below:
▼ DOWNLOAD Spyhunter By downloading any software listed on this website you agree to our Privacy Policy and Terms of Use. Free scanner checks if your computer is infected. To remove malware, you have to purchase the full version of Spyhunter.

Quick menu:

Step 1

Windows XP and Windows 7 users: Start your computer in Safe Mode. Click Start, click Shut Down, click Restart, click OK. During your computer start process, press the F8 key on your keyboard multiple times until you see the Windows Advanced Option menu, and then select Safe Mode with Networking from the list.

Safe Mode with Networking

Video showing how to start Windows 7 in "Safe Mode with Networking":

Windows 8 users: Start Windows 8 is Safe Mode with Networking - Go to Windows 8 Start Screen, type Advanced, in the search results select Settings. Click Advanced startup options, in the opened "General PC Settings" window, select Advanced startup. Click the "Restart now" button. Your computer will now restart into the "Advanced Startup options menu". Click the "Troubleshoot" button, and then click the "Advanced options" button. In the advanced option screen, click "Startup settings". Click the "Restart" button. Your PC will restart into the Startup Settings screen. Press F5 to boot in Safe Mode with Networking.

Windows 8 Safe Mode with networking

Video showing how to start Windows 8 in "Safe Mode with Networking":

Windows 10 users: Click the Windows logo and select the Power icon. In the opened menu click "Restart" while holding "Shift" button on your keyboard. In the "choose an option" window click on the "Troubleshoot", next select "Advanced options". In the advanced options menu select "Startup Settings" and click on the "Restart" button. In the following window you should click the "F5" button on your keyboard. This will restart your operating system in safe mode with networking.

windows 10 safe mode with networking

Video showing how to start Windows 10 in "Safe Mode with Networking":

Step 2

Log in to the account infected with the Mosk virus. Start your Internet browser and download a legitimate anti-spyware program. Update the anti-spyware software and start a full system scan. Remove all entries detected.

If you cannot start your computer in Safe Mode with Networking, try performing a System Restore.

Video showing how to remove ransomware virus using "Safe Mode with Command Prompt" and "System Restore":

1. During your computer start process, press the F8 key on your keyboard multiple times until the Windows Advanced Options menu appears, and then select Safe Mode with Command Prompt from the list and press ENTER.

Boot your computer in Safe Mode with Command Prompt

2. When Command Prompt mode loads, enter the following line: cd restore and press ENTER.

system restore using command prompt type cd restore

3. Next, type this line: rstrui.exe and press ENTER.

system restore using command prompt rstrui.exe

4. In the opened window, click "Next".

restore system files and settings

5. Select one of the available Restore Points and click "Next" (this will restore your computer system to an earlier time and date, prior to the Mosk ransomware virus infiltrating your PC).

select a restore point

6. In the opened window, click "Yes".

run system restore

7. After restoring your computer to a previous date, download and scan your PC with recommended malware removal software to eliminate any remaining Mosk ransomware files.

To restore individual files encrypted by this ransomware, try using Windows Previous Versions feature. This method is only effective if the System Restore function was enabled on an infected operating system. Note that some variants of Mosk are known to remove Shadow Volume Copies of the files, so this method may not work on all computers.

To restore a file, right-click over it, go into Properties, and select the Previous Versions tab. If the relevant file has a Restore Point, select it and click the "Restore" button.

Restoring files encrypted by CryptoDefense

If you cannot start your computer in Safe Mode with Networking (or with Command Prompt), boot your computer using a rescue disk. Some variants of ransomware disable Safe Mode making its removal complicated. For this step, you require access to another computer.

To regain control of the files encrypted by Mosk, you can also try using a program called Shadow Explorer. More information on how to use this program is available here.

shadow explorer screenshot

To protect your computer from file encryption ransomware such as this, use reputable antivirus and anti-spyware programs. As an extra protection method, you can use programs called HitmanPro.Alert and EasySync CryptoMonitor, which artificially implant group policy objects into the registry to block rogue programs such as Mosk ransomware.

Note that Windows 10 Fall Creators Update includes a "Controlled Folder Access" feature that blocks ransomware attempts to encrypt your files. By default, this feature automatically protects files stored in the Documents, Pictures, Videos, Music, Favorites, and Desktop folders.

Controll Folder Access

Windows 10 users should install this update to protect their data from ransomware attacks. Here is more information on how to get this update and add an additional protection layer from ransomware infections.

HitmanPro.Alert CryptoGuard - detects encryption of files and neutralises any attempts without need for user-intervention:

hitmanproalert ransomware prevention application

Malwarebytes Anti-Ransomware Beta uses advanced proactive technology that monitors ransomware activity and terminates it immediately - before reaching users' files:

malwarebytes anti-ransomware

  • The best way to avoid damage from ransomware infections is to maintain regular up-to-date backups. More information on online backup solutions and data recovery software Here.

Other tools known to remove Mosk ransomware:

About the author:

Tomas Meskauskas

Tomas Meskauskas - expert security researcher, professional malware analyst.

I am passionate about computer security and technology. I have an experience of over 10 years working in various companies related to computer technical issue solving and Internet security. I have been working as an author and editor for since 2010. Follow me on Twitter and LinkedIn to stay informed about the latest online security threats. Contact Tomas Meskauskas.

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Malware activity

Global malware activity level today:

Medium threat activity

Increased attack rate of infections detected within the last 24 hours.

QR Code
Mosk virus QR code
A QR code (Quick Response Code) is a machine-readable code which stores URLs and other information. This code can be read using a camera on a smartphone or a tablet. Scan this QR code to have an easy access removal guide of Mosk virus on your mobile device.
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Platform: Windows

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