How to uninstall Nosu ransomware from the operating system?

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

Nosu ransomware removal instructions

What is Nosu?

Nosu is a part of Djvu ransomware family. Like most programs of this type, Nosu is designed to prevent victims from accessing their files unless a ransom is paid. It encrypts data, creates a ransom note ("_readme.txt" text file) and appends the ".nosu" extension to a filename of every encrypted file. For example, it renames "1.jpg" to "1.jpg.nosu", and so on.

As explained in the "_readme.txt" text file, Nosu encrypts files with a strong encryption algorithm and unique key. The only way to recover files is by using a decryption tool and key that can be purchased from Nosu developers for $490 if they will be contacted in 72 hours after encryption. It is mentioned that after 72 hours price of those decryption tools is going to be increased to $980, which means victims are encouraged to contact Nosu developers as soon as possible. They can be contacted by writing them an email (with the appointed personal ID in it) to helpmanager@firemail.cc or helpmanager@iran.ir. When contacted, they supposed to send further instructions on how to pay for a decryption tool and key. Typically, cyber criminals want to be paid in cryptocurrency. In one way or another, it is not recommended to trust (pay) them because victims who trust them often become victim of a scam. Simply said, cyber criminals do not send decryption tool and/or key even after a payment. Unfortunately, there are no free tools that could decrypt files encrypted by Nosu, at least not at the moment. In such cases the only way to recover files for free/without using tools that only developers of a particular ransomware have is to restore them from a backup. Also, it is worth mentioning that files remain encrypted even after removal of ransomware. Its removal only prevents it from causing further encryptions.

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

Nosu decrypt instructions (_readme.txt)

Nosu operates like many other ransomware-type programs (e.g., BWNG, Mark, 5ss5c). Typically, these programs block access to data by encrypting it and provide victims with instructions on how to pay a ransom. Two main variables usually are price of decryption tool and/or key and cryptographic algorithm (symmetric or asymmetric) that ransomware uses to lock victim's files. Unfortunately, most of the times it is impossible to decrypt files without a tool and/or key that can be provided only by developers of a particular ransomware. Free decryptions are possible only in cases when ransomware contains some bugs, flaws, and other vulnerabilities. That is why it is important to have a data backup. Also, it should be kept on a remote server and/or unplugged storage device so it could not be encrypted with the rest of the files.

How did ransomware infect my computer?

Typically, computers get infected with ransomware and other malware through spam campaigns, Trojans, untrustworthy software download sources, fake software updaters and unofficial software activation tools. Cyber criminals spread malware via spam campaigns by sending emails that contain malicious attachments or website links that are designed to download some malicious file. Typically, those attachments/files, if opened, install malicious software. In most cases cyber criminals attach PDF documents, archive files (like RAR, ZIP), executables (.exe files), Microsoft Office documents and JavaScript files. Trojans are malicious programs that usually are designed to cause chain infections. When a program of this type is installed, it installs some other program of this kind. Examples of untrustworthy software download sources that could be used to spread malware are: freeware download websites, free file hosting pages, Peer-to-Peer networks (e.g., torrent clients, eMule), third party downloaders, unofficial websites, and so on. People who download files through them risk to download some malicious file that, if opened, would install malware. Fake software updaters infect operating systems by exploiting bugs, flaws and other vulnerabilities of some outdated software that is installed on the operating system, or by simply installing malicious programs instead of updates. Unofficial software activation ('cracking') tools are programs that supposed to bypass paid activation of licensed software. Nevertheless, programs of this type can be (and often are) designed to install malicious software.

Threat Summary:
Name Nosu virus
Threat Type Ransomware, Crypto Virus, Files locker
Encrypted Files Extension .nosu
Ransom Demanding Message _readme.txt
Ransom Amount $980/$490
Cyber Criminal Contact helpmanager@firemail.cc, helpmanager@iran.ir
Detection Names Avast (Win32:TrojanX-gen [Trj]), BitDefender (Gen:Variant.Razy.601173), ESET-NOD32 (A Variant Of Win32/Kryptik.HAIP), Kaspersky (Trojan-Ransom.Win32.Stop.if), Full List Of Detections (VirusTotal)
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).
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.
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.
Removal

To eliminate Nosu 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?

We recommend to download files and software only from official websites (and via direct download links). None of the aforementioned and other similar sources can be trusted, they may be used by cyber criminals as tools to proliferate various malicious programs. If a received email irrelevant, it is received from suspicious, unknown address and it contains some web link or attachment, then its contents should not be opened. Also, it is worth mentioning that cyber criminals often disguise their emails as official, important, and so on. All installed software must be updated and activated (if necessary) through tools and/or implemented functions that are provided/designed by official developers. Other tools can be designed to install malware. Besides, it is not legal to activate software through unofficial activation tools. And finally, we recommend to scan the operating system for threats regularly and do that by using a reputable antivirus or anti-spyware software. If your computer is already infected with Nosu, we recommend running a scan with Spyhunter for Windows to automatically eliminate this ransomware.

Text presented in Nosu ransomware's 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:
https://we.tl/t-Oc0xgfzC7q
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:
helpmanager@firemail.cc

 

Reserve e-mail address to contact us:
helpmanager@iran.ir

 

Your personal ID:

-

Screenshot of files encrypted by Nosu (".nosu" extension):

Files encrypted by Nosu ransomware (.nosu extension)

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

Fake Windows pop-up displayed by pavadinimas during the encryption

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 (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:

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 not supported anymore. 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's variants and you can find more information, as well as download link and decryption instructions in Emsisoft's official 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 pair of the same file before and after the encryption. All victims have to do is upload a pair of original and encrypted file to Emsisoft's Djvu decryption page and download the aforementioned decryption tool (the download link will be provided after uploading files). Note that the file processing may take some time so be patient. It is also worth mentioning that the system must have an Internet connection during the entire decryption process, otherwise it will fail.

Screenshot of Emsisoft's Djvu decryption service page:

Djvu ransomware decryption service by Emsisoft

Nosu ransomware removal:

Instant automatic removal of Nosu 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 Nosu 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 Nosu 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 Nosu 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 Nosu 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 Nosu 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 Nosu, 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 Nosu 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 Nosu 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 pcrisk.com since 2010. Follow me on Twitter and LinkedIn to stay informed about the latest online security threats. Contact Tomas Meskauskas.

PCrisk security portal is brought by a company RCS LT. Joined forces of security researchers help educate computer users about the latest online security threats. More information about the company RCS LT.

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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
Nosu virus QR code
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Platform: Windows

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