How to remove Cosw Ransomware and decrypt .cosw files

What is Cosw Ransomware

New instances of STOP Ransomware (DjVu Ransomware) continue to damage users files all over the world. STOP/Djvu Ransomware is a specific type of ransomware that has been active since 2017. It is a type of file-encrypting malware that encrypts victims’ files and demands payment in exchange for the decryption key. This crypto-virus uses a complex AES encryption algorithm to block users’ access to their data and extort a ransom of $490 or $980. One of the new variations of extension, that appeared in October 2022, is: .cosw. Corresponding ransomware got the name Cosw Ransomware. The virus adds such suffixes to the end of encrypted files. If your files got such an ending and are not accessible, it means your PC is infected with STOP Ransomware. Malware developers slightly modify the virus technically. They just create new extensions and are using the same ransom note, called _readme.txt during this year:

As you can see from the message above, hackers offer to decrypt 1 file for free and provide a “discount” if the user pays within the first 72 hours. However, those are, often, false promises, and malefactors do not reply after receiving the payment. Luckily, in some cases, your files can be decrypted. This can be possible if there was some internet connection loss or malfunction of the hacker’s servers during the encryption process. In this situation, Cosw Ransomware uses an offline key, that can be calculated by a special tool called STOP Djvu Decryptor. Please, download it below, and read the instructions on how to use it carefully. If STOP Djvu Decryptor is unable to help you, you can try some alternative methods to restore your photos, documents, videos, etc. There are standard Windows system functions, such as restore points, shadow copies, previous versions of files, which can be useful, although, malicious algorithms often prevent such opportunities. Stellar Data Recovery Professional is one of the best file-recovery tools and, if used properly, may recover some copies of encrypted files, that were removed earlier. This is a comprehensive tutorial on how to remove Cosw Ransomware and decrypt .cosw files using all available methods and utilities.

How Cosw Ransomware infected your computer

The STOP/Djvu ransomware is typically spread through malicious email attachments, software cracks or keygens, or through exploit kits that take advantage of vulnerabilities in software or operating systems.

1. Download Cosw Ransomware Removal Tool
2. Get decryption tool for .cosw files
3. Recover encrypted files with Stellar Data Recovery Professional
4. Restore encrypted files with Windows Previous Versions
5. Restore files with Shadow Explorer
6. Restore media files with Media Repair
7. How to protect from threats like Cosw Ransomware

Virus modifies “hosts” file to block Windows updates, downloading antivirus programs, and visiting sites related to security news or offering security solutions. Cosw Ransomware comes along with AZORult trojan, which was initially created to steal logins and passwords. The process of infection also looks like installing Windows updates, the malware shows a fake window, that mimics the update process.

It uses rdpclip.exe to replace a legal Windows file and to launch an attack on a computer network. After encrypting the files, the encrypter is deleted using the delself.bat command file. Cosw Ransomware virus is propagated via spam attack with malicious e-mail attachments and using manual PC hacking. Can be distributed by hacking through an unprotected RDP configuration, fraudulent downloads, exploits, web injections, fake updates, repackaged, and infected installers. The virus assigns a certain ID to the victims, which is used to name those files and supposedly to send a decryption key. Great tools to protect against Cosw Ransomware are: Emsisoft Anti-Malware and Malwarebytes Anti-Malware.

How to remove Cosw Ransomware manually

It is not recommended to remove Cosw Ransomware manually, for safer solution use Removal Tools instead.

Cosw Ransomware files:

_readme.txt
rdpclip.exe
delself.bat
{randomname}.exe

Cosw Ransomware registry keys:

no information

How to decrypt and restore .cosw files

Use automated decryptors

Download STOP Djvu Decryptor from EmsiSoft (.cosw variations)

IMPORTANT: Read this detailed guide on using STOP Djvu Decryptor to avoid file corruption and time wasting.

STOP Djvu Decryptor is able to decrypt .cosw files, encrypted by Cosw Ransomware. This tool was developed by EmsiSoft. It works in automatic mode, but in most cases works only for files encrypted with offline keys. Download it here:

Download STOP Djvu Decryptor

Dr.Web Rescue Pack

Famous antivirus vendor Dr. Web provides free decryption service for the owners of its products: Dr.Web Security Space or Dr.Web Enterprise Security Suite. Other users can ask for help in the decryption of .cosw files by uploading samples to Dr. Web Ransomware Decryption Service. Analysis of files will be performed free of charge and if files are decryptable, all you need to do is purchase a 2-year license of Dr.Web Security Space worth $120 or less. Otherwise, you don’t have to pay.

If you are infected with Cosw Ransomware and removed it from your computer, you can try decrypting your files. Antivirus vendors and individuals create free decryptors for some crypto-lockers. To attempt to decrypt them manually you can do the following:

Use Stellar Data Recovery Professional to restore .cosw files

1. Download Stellar Data Recovery Professional.
2. Click Recover Data button.
3. Select type of files you want to restore and click Next button.
4. Choose location where you would like to restore files from and click Scan button.
5. Preview found files, choose ones you will restore and click Recover.

Download Stellar Data Recovery Professional

Using Windows Previous Versions option:

1. Right-click on infected file and choose Properties.
2. Select Previous Versions tab.
3. Choose particular version of the file and click Copy.
4. To restore the selected file and replace the existing one, click on the Restore button.
5. In case there is no items in the list choose alternative method.

Using Shadow Explorer:

1. Download Shadow Explorer program.
2. Run it and you will see screen listing of all the drives and the dates that shadow copy was created.
3. Select the drive and date that you want to restore from.
4. Right-click on a folder name and select Export.
5. In case there are no other dates in the list, choose alternative method.

If you are using Dropbox:

1. Login to the DropBox website and go to the folder that contains encrypted files.
2. Right-click on the encrypted file and select Previous Versions.
3. Select the version of the file you wish to restore and click on the Restore button.

Use Media Repair to decrypt media files encrypted with .cosw

1. Download Media Repair tool.
2. Right-click on the downloaded archive, and select Extract to Media_Repair\.
3. Then double-click on the extracted .exe file to launch the utility.
4. At first, you have to choose which file type you want to decrypt. You can do it from the drop-down menu in the utility.
5. Next, browser the folder with encrypted or reference files. Choose any of them and click on the Test icon located in the top right corner.
6. Media Repair will display a pop-up message with information on whether it can repair the selected file or not.
7. After checking if it is possible or not, select your reference file and click on the icon right under the Test button we used in step #5.
8. If the file pair is properly matched, you can move on and hit the Play button to start repairing. You can also stop the process anytime by clicking on the Stop button.

How to protect computer from viruses, like Cosw Ransomware, in future

1. Get special anti-ransomware software

Use ZoneAlarm Anti-Ransomware

Famous antivirus brand ZoneAlarm by Check Point released a comprehensive tool, that will help you with active anti-ransomware protection, as an additional shield to your current protection. The tool provides Zero-Day protection against ransomware and allows you to recover files. ZoneAlarm Anti-Ransomware is compatible with all other antiviruses, firewalls, and security software except ZoneAlarm Extreme (already shipped with ZoneAlarm Anti-Ransomware) or Check Point Endpoint products. The killer features of this application are: automatic file recovery, overwrite protection that instantly and automatically recovers any encrypted files, file protection that detects and blocks even unknown encryptors.

Download ZoneAlarm Anti-Ransomware

2. Back up your files

As an additional way to save your files, we recommend online backup. Local storage, such as hard drives, SSDs, flash drives, or remote network storage can be instantly infected by the virus once plugged in or connected to. Cosw Ransomware uses some techniques to exploit this. One of the best services and programs for easy automatic online backup is iDrive. It has the most profitable terms and a simple interface. You can read more about iDrive cloud backup and storage here.

Download iDrive

3. Do not open spam e-mails and protect your mailbox

Malicious attachments to spam or phishing e-mails are the most popular method of ransomware distribution. Using spam filters and creating anti-spam rules is good practice. One of the world leaders in anti-spam protection is MailWasher Pro. It works with various desktop applications and provides a very high level of anti-spam protection.

Download MailWasher Pro