Cosanostra Ransomware

Also Known As: Cosanostra virus
Distribution: Low
Damage level: Severe

Cosanostra ransomware removal instructions

What is Cosanostra?

Cosanostra is a malicious program classified as ransomware. Once a computer is infected, users lose access to their files due to encryption. This allows cyber criminals (in this case, Cosanostra's developers) to blackmail victims and demand ransom payments. This particular ransomware is a new variant of Garrantydecrypt and was discovered by MalwareHunterTeam. Cosanostra adds the ".cosanostra" extension to each encrypted file. For example, "1.jpg" becomes "1.jpg.cosanostra", and so on. This malicious program also creates a ransom message called "#RECOVERY_FILES#", which is presented in a text (.txt) file.

The text file ("#RECOVERY_FILES#.txt") states that Cosanostra was used to encrypt all files stored on the computer. To decrypt them, victims must send an email to the cyber criminals at, which must contain a personal (unique) ID number that is assigned to each Cosanostra victim. Sending this email gives an indication to the criminals that victims are willing to pay the required ransom sum to purchase a decryption tool. The cost of decryption tool is not specified, however, the ransom message states that this depends on how quickly victims make contact. It is also stated that victims must transfer the ransom sum in the Bitcoin cryptocurrency. They promise to send a decryption tool as soon as they receive the payment. Be aware that it is very unlikely that they will keep this promise. Cyber criminals generally ignore victims and send no decryption tools (even if ransoms are paid). Unfortunately, only they can provide this tool, since they use cryptography algorithms (symmetric or asymmetric) that generate unique decryption keys - only a specific tool is capable of decryption. Thus, decryption without the involvement of ransomware developers is impossible. As there are no tools capable of file free decryption, we recommend that you use a data backup if one was created prior to computer infection by Cosanostra.

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

Cosanostra decrypt instructions

There are many ransomware-type infections online, including examples such as ETH and Qwex. These programs encrypt data and make ransom demands. The only differences are usually cost of decryption tool and cryptography algorithm used for encryption. Generally, cyber criminals use cryptographies that are impossible to 'crack'/decrypt without using their tools (unless ransomware is still in development or has bugs/flaws that are not fixed). To prevent data loss caused by these programs, generate regular backups and keep them stored on remote servers or unplugged storage devices. If not, they might be encrypted together with all other data stored on the computer.

How did ransomware infect my computer?

Typically, ransomware developers proliferate these malicious programs through untrustworthy software download sources, fake software updaters, spam (email) campaigns, Trojans and software cracking tools. Examples of untrustworthy software download sources are Peer-to-Peer (P2P) networks (torrent clients, eMule, and others), freeware download websites, file hosting websites and unofficial (dubious) websites. These sources are present malicious programs as legitimate. Cyber criminals use them to trick people into downloading and installing high-risk computer infections. Unofficial (fake) software updaters often download and install malicious programs rather than the software updates or fixes offered. These tools might also be used to exploit bugs/flaws of outdated software. Cyber criminals use spam campaigns to trick people into downloading and opening the presented malicious attachments (they send emails that usually contain attachments or web links). Opening them leads to unwanted downloads and installations. Attached files are usually MS Office documents (such as Word, Excel etc.), archive files (ZIP, RAR), PDF documents, executable (.exe) files, and so on. Trojans are malicious programs that must first be installed to cause infections. These programs go on to cause chain infections (proliferate other infections). Some cyber criminals use software cracking tools to proliferate ransomware (or other threats). These tools usually activate software without payment, however, cyber criminals employ them to infect computers. Rather than activating software (or operating systems), they install malicious programs.

Threat Summary:
NameCosanostra virus
Threat TypeRansomware, Crypto Virus, Files locker
SymptomsCan't open files stored on your computer, previously functional files now have a different extension, for example my.docx.locked. A ransom demanding message is displayed on your desktop. Cyber criminals are asking to pay a ransom (usually in bitcoins) to unlock your files.
Distribution methodsInfected email attachments (macros), torrent websites, malicious ads.
DamageAll 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 Cosanostra virus our malware researchers recommend scanning your computer with Spyhunter.
▼ Download Spyhunter
Free scanner checks if your computer is infected. To remove malware, you have to purchase the full version of Spyhunter.

How to protect yourself from ransomware infections?

To prevent computer infection with ransomware-type (and other) infections, carefully analyze emails that contain attachments (or web links). If a received email seems irrelevant or is sent from an unknown, suspicious address, do not download or open the presented attachment, or open the web link. Update software using implemented functions or tools provided by official software developers. Other tools should not be trusted or used. Download applications, files, and software using official websites or other reliable sources. Do not use third party channels/sources - they are often used to distribute rogue downloaders/installers or even malicious programs. The same applies to software cracking tools: people who use these tools commit a cyber crime and risk computer infection with ransomware (or other infections) rather than bypassing software (or operating system) paid activation. Have a reputable anti-virus or anti-spyware suite installed and active (enabled). These tools are helpful when dealing with various infections: they often detect and remove threats before any damage to the system is done. If your computer is already infected with Cosanostra, we recommend running a scan with Spyhunter for Windows to automatically eliminate this ransomware.

Text presented in Cosanostra ransomware text file ("#RECOVERY_FILES#.txt"):

All your files have been encrypted!
Now you should send us email with your personal identifier.
This email will be as confirmation you are ready to pay for decryption key.
You have to pay for decryption in Bitcoins. The price depends on how fast you write
to us.
After payment we will send you the decryption tool that will decrypt all your files.

Contact us using this email address
And tell us your unique ID

Screenshot of files encrypted by Cosanostra (".cosanostra" extension):

Files encrypted by Cosanostra

Cosanostra ransomware removal:

Instant automatic removal of Cosanostra 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 Cosanostra 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 Cosanostra 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 Cosanostra 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 Cosanostra 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 Cosanostra 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 Cosanostra, 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 Cosanostra 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 as well as 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 Cosanostra ransomware: