How to remove MOSK ransomware (Virus Removal Guide)

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Written by: Stelian Pilici

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If you cannot open your images, documents, or files and they have a “.mosk” extension, then your computer is infected with the STOP/DJVU ransomware.

The STOP/DJVU ransomware encrypts the personal documents found on the victim’s computer, then displays a message which offers to decrypt the data if payment in Bitcoin is made. The instructions are placed on the victim’s desktop in the _readme.txt file.

Image: Mosk Ransomware Virus
Image: Mosk Ransomware

1. What is the Mosk ransomware?

Mosk is a file-encrypting ransomware infection that restricts access to data (files, images, videos) by encrypting files with the “.mosk” extension. It then attempts to extort money from victims by asking for “ransom”, in the form of Bitcoin cryptocurrency, in exchange for access to data.

This ransomware targets all versions of Windows including Windows 7, Windows 8.1 and Windows 10. When this ransomware is first installed on a computer it will create a random named executable in the %AppData% or %LocalAppData% folder. This executable will be launched and begin to scan all the drive letters on your computer for data files to encrypt.

STOP/DJVU ransomware searches for files with certain file extensions to encrypt. The files it encrypts include important productivity documents and files such as .doc, .docx, .xls, .pdf, among others. When these files are detected, this infection will change the extension to Mosk, so they are no longer able to be opened.

The STOP/DJVU ransomware changes the name of each encrypted file to the following format: name.mosk

Once your files are encrypted with the .mosk extension, you cannot open these files and this ransomware will create the info.txt ransom note in each folder that a file has been encrypted and on the Windows desktop.
When the infection has finished scanning your computer it will also delete all of the Shadow Volume Copies that are on the affected computer. It does this so that you cannot use the shadow volume copies to restore your encrypted files.

2. How did the Mosk ransomware get on my computer?

The Mosk ransomware is distributed via spam email containing infected attachments or by exploiting vulnerabilities in the operating system and installed programs.

Cyber-criminals spam out an email, with forged header information, tricking you into believing that it is from a shipping company like DHL or FedEx. The email tells you that they tried to deliver a package to you, but failed for some reason. Sometimes the emails claim to be notifications of a shipment you have made. Either way, you can’t resist being curious as to what the email is referring to – and open the attached file (or click on a link embedded inside the email). And with that, your computer is infected with the Mosk ransomware.

This ransomware was also observed attacking victims by hacking open Remote Desktop Services (RDP) ports. The attackers scan for the systems running RDP (TCP port 3389) and then attempt to brute force the password for the systems.

3. Is my computer infected with Mosk Ransomware?

Here is a short summary for the Mosk ransomware:

  • Ransomware family: STOP/DJVU ransomware
  • Extensions: .mosk
  • Ransomware note: _readme.txt
  • Ransom: From $490 to $980 (in Bitcoins)
  • Contact: salesrestoresoftware@firemail.cc, salesrestoresoftware@gmail.com
  • Symptoms: Your files have a .mosk extension and cannot be opened by any programs

When this ransomware infects your computer it will scan all the drive letters for targeted file types, encrypt them, and then append the “.mosk” extension to them. Once these files are encrypted, they will no longer able to be opened by your normal programs. When this ransomware has finished encrypting the victim’s files, it will also display a ransom note that includes instructions on how to contact these cybercriminals (salesrestoresoftware@firemail.cc or salesrestoresoftware@gmail.com).

This is the message that the Mosk ransomware (_readme.txt) will display:

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:
https://we.tl/t-IbdGyCKhdr
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:
salesrestoresoftware@firemail.cc

Reserve e-mail address to contact us:
salesrestoresoftware@gmail.com

If your computer is infected with this ransomware, we recommend that you contact the following government fraud and scam sites to report this attack:

If your country or region isn’t listed here, we recommend that you contact your country or region’s federal police or communications authority.

4. How to remove the Mosk ransomware and recover the files

It’s important to understand that by starting the removal process you risk losing your files, as we cannot guarantee that you will be able to recover them. Your files may be permanently compromised when trying to remove this infection or trying to recover the encrypted documents. We cannot be held responsible for losing your files or documents during this removal process.

This guide was written to help you remove the infection itself from your computer, and if a 100% proven method to recover the encrypted files is found we will update this guide.

STEP 1: Use Malwarebytes to remove Mosk ransomware

Malwarebytes is one of the most popular and most used anti-malware software for Windows, and for good reasons. It is able to destroy many types of malware that other software tends to miss, without costing you absolutely nothing. When it comes to cleaning up an infected device, Malwarebytes has always been free and we recommend it as an essential tool in the fight against malware.

The first time you install Malwarebytes, you’re given a free 14-day trial of the premium edition, which includes preventative tools like real-time scanning and specific protection from ransomware. After two weeks, it automatically reverts to the basic free version that will detect and clean up malware infections only when you run a scan. It is important to note that Malwarebytes will run alongside antivirus software without conflicts.

  1. Download Malwarebytes.

    You can download Malwarebytes by clicking the link below.

    MALWAREBYTES DOWNLOAD LINK
    (The above link open a new page from where you can download Malwarebytes)

  2. Double-click on the Malwarebytes setup file.

    When Malwarebytes has finished downloading, double-click on the mb3-setup-consumer-x.x.x.xxxx.exe file to install Malwarebytes on your PC. In most cases, downloaded files are saved to the Downloads folder.

    Double-click on mb3-setup to install Malwarebytes Help
    You may be presented with a User Account Control pop-up asking if you want to allow Malwarebytes to make changes to your device. If this happens, you should click “Yes” to continue with the installation.
    Windows asking for permission to run the Malwarebytes installer - Help Guide

  3. Follow the on-screen prompts to install Malwarebytes.

    When the Malwarebytes installation begins, you will see the Malwarebytes Setup Wizard which will guide you through the installation process. To install Malwarebytes on your PC, click on the “Agree and Install” button.
    Malwarebytes Setup Screen - Help Guide
    Malwarebytes is installed on your PC - Help Guide

  4. Click on “Scan Now”.

    Once installed, Malwarebytes will automatically start and update the antivirus database. To perform a system scan, click on the “Scan Now” button.
    Start a scan with Malwarebytes

  5. Wait for the Malwarebytes scan to complete.

    Malwarebytes will now start scanning your computer for adware and other malicious programs. This process can take a few minutes, so we suggest you do something else and periodically check on the status of the scan to see when it is finished.
    Malwarebytes scanning PC for Mosk malware

  6. Click on “Quarantine Selected”.

    When the scan has completed, you will be presented with a screen showing the malware infections that Malwarebytes has detected. To remove the malicious programs that Malwarebytes has found, click on the “Quarantine Selected” button.
    Click on the Quarantine Selected button to remove Mosk virus

  7. Reboot your computer.

    Malwarebytes will now remove all the malicious files and registry keys that it has found. To complete the malware removal process, Malwarebytes may ask you to restart your computer.
    Malwarebytes requesting to restart computer to complete malware removal process - Help Guide
    When the malware removal process is complete, you can close Malwarebytes and continue with the rest of the instructions.

STEP 2: Use Emsisoft Emergency Kit to scan for malware and unwanted programs

Emsisoft Emergency Kit is a free second opinion scanner that can be used without installation to scan and clean infected computers. Emsisoft scans the behavior of active files and also files in locations where malware normally resides for suspicious activity.

  1. Download Emsisoft Emergency Kit.

    You can download Emsisoft Emergency Kit by clicking the link below.

    EMSISOFT EMERGENCY KIT DOWNLOAD LINK
    (The above link will open a new web page from where you can download Emsisoft Emergency Kit)

  2. Install Emsisoft Emergency Kit.

    Double-click on the EmsisoftEmergencyKit setup file to start the installation process, then click on the “Install” button.
    Click on the Install button

  3. Start Emsisoft Emergency Kit.

    On your desktop the “EEK” folder (C:\EEK) should now be open. To start Emsisoft, click on the “Start Emsisoft Emergency Kit” file to open this program.
    Click on Start Emsisoft Emergency Kit

    You may be presented with a User Account Control dialog asking you if you want to run this file. If this happens, you should click “Yes” to continue with the installation.
    Allow Emsisoft to run on your PC - UAC

  4. Click on “Malware Scan”.

    Emsisoft Emergency Kit will start and it will ask you for permission to update itself. Once the update process is complete, click on the “Scan” tab, and perform a “Malware Scan“.

    Perform a Malware Scan with Emsisoft Emergency Kit
    Emsisoft Emergency Kit will now scan your PC for malicious files. This process can take a few minutes.
    Emsisoft Emergency Kit Scanning

  5. Click on “Quarantine selected”.

    When the Emsisoft scan has finished, you will be presented with a screen reporting which malicious files were detected on your computer. To remove the malicious programs, click on the “Quarantine selected“.
    Click on Quarantine Selected to remove the malicious programs
    When the malware removal process is complete, Emsisoft Emergency Kit may need to restart your computer. Click on the “Restart” button to restart your computer.
    When the process is complete, you can close Emsisoft and continue with the rest of the instructions.

STEP 3: Restore the files encrypted by Mosk ransomware with Emsisoft Decryptor for STOP Djvu

Unfortunately, in most cases, it’s not possible to recover the files encrypted by this ransomware because the private key which is needed to unlock the encrypted files is only available through the cybercriminals.
However, if your files were encrypted with an offline key there is a chance you can recover them by using Emsisoft Decryptor for STOP Djvu decryption tool.
Here’s how to recover your files using the Emsisoft Decryptor for STOP Djvu.

Make sure you remove the malware from your computer first, otherwise, it will repeatedly lock your system or encrypt files. If you suspect that your computer is still infected with malware, you can run a free scan with ESET Online Scanner.

  1. Download Emsisoft Decryptor for STOP Djvu

    You can download Emsisoft Decryptor for STOP Djvu by clicking the link below.

    EMSISOFT DECRYPTOR FOR STOP DJVU DOWNLOAD LINK
    (The above link will open a new web page from where you can download Emsisoft Decryptor for STOP Djvu)

  2. Run Emsisoft Decryptor for STOP Djvu

    When Emsisoft Decryptor for STOP Djvu has finished downloading, double-click on “decrypt_STOPDjvu.exe” to run this program on your computer. In most cases, downloaded files are saved to the Downloads folder.

    Double-click on the Emsisoft Decryptor for STOP Djvu icon

    You may be presented with a User Account Control pop-up asking if you want to allow Emsisoft to make changes to your device. If this happens, you should click “Yes” to continue with the installation.

  3. Follow the on-screen prompts

    When the Emsisoft Decryptor for STOP Djvu starts, you will need to agree with the Terms and accept a disclaimer.
    Click Yes to Continue

  4. Click on “Decrypt”.

    Click the “Decrypt” button to start the decryption process. The screen will switch to a status view, informing you about the current process and decryption status of your files.

    Click Decrypt to recover your files

  5. The decryptor will inform you once the decryption process is finished. If you require the report for your personal records, you can save it by clicking the “Save log” button. If your system was compromised through the Windows Remote Desktop feature, we also recommend changing all passwords of all users that are allowed to login remotely and check the local user accounts for additional accounts the attacker might have added.

Unfortunately, in most cases, it’s not possible to recover the files encrypted by the Mosk ransomware because the private key which is needed to unlock the encrypted files is only available through the cybercriminals.

Do not pay any money to recover your files. Even if you were to pay the ransom, there is no guarantee that you will regain access to your files.

Your computer should now be free of the Mosk ransomware infection. If you are still experiencing problems while trying to remove Mosk ransomware from your computer, please do one of the following:

How to Stay Safe Online

Here are 10 basic security tips to help you avoid malware and protect your device:

  1. Use a good antivirus and keep it up-to-date.

    Shield Guide

    It's essential to use a good quality antivirus and keep it up-to-date to stay ahead of the latest cyber threats. We are huge fans of Malwarebytes Premium and use it on all of our devices, including Windows and Mac computers as well as our mobile devices. Malwarebytes sits beside your traditional antivirus, filling in any gaps in its defenses, and providing extra protection against sneakier security threats.

  2. Keep software and operating systems up-to-date.

    updates-guide

    Keep your operating system and apps up to date. Whenever an update is released for your device, download and install it right away. These updates often include security fixes, vulnerability patches, and other necessary maintenance.

  3. Be careful when installing programs and apps.

    install guide

    Pay close attention to installation screens and license agreements when installing software. Custom or advanced installation options will often disclose any third-party software that is also being installed. Take great care in every stage of the process and make sure you know what it is you're agreeing to before you click "Next."

  4. Install an ad blocker.

    Ad Blocker

    Use a browser-based content blocker, like AdGuard. Content blockers help stop malicious ads, Trojans, phishing, and other undesirable content that an antivirus product alone may not stop.

  5. Be careful what you download.

    Trojan Horse

    A top goal of cybercriminals is to trick you into downloading malware—programs or apps that carry malware or try to steal information. This malware can be disguised as an app: anything from a popular game to something that checks traffic or the weather.

  6. Be alert for people trying to trick you.

    warning sign

    Whether it's your email, phone, messenger, or other applications, always be alert and on guard for someone trying to trick you into clicking on links or replying to messages. Remember that it's easy to spoof phone numbers, so a familiar name or number doesn't make messages more trustworthy.

  7. Back up your data.

    backup sign

    Back up your data frequently and check that your backup data can be restored. You can do this manually on an external HDD/USB stick, or automatically using backup software. This is also the best way to counter ransomware. Never connect the backup drive to a computer if you suspect that the computer is infected with malware.

  8. Choose strong passwords.

    lock sign

    Use strong and unique passwords for each of your accounts. Avoid using personal information or easily guessable words in your passwords. Enable two-factor authentication (2FA) on your accounts whenever possible.

  9. Be careful where you click.

    cursor sign

    Be cautious when clicking on links or downloading attachments from unknown sources. These could potentially contain malware or phishing scams.

  10. Don't use pirated software.

    Shady Guide

    Avoid using Peer-to-Peer (P2P) file-sharing programs, keygens, cracks, and other pirated software that can often compromise your data, privacy, or both.

To avoid potential dangers on the internet, it's important to follow these 10 basic safety rules. By doing so, you can protect yourself from many of the unpleasant surprises that can arise when using the web.

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