BTOS ransomware targets inattentive Windows users to encrypt their files
Contents
BTOS ransomware is a malicious virus designed to encrypt personal files on Windows operating systems. It is the 202nd version of STOP/DJVU virus. The ransomware encrypts files using RSA and marks them with .btos file extensions. The virus then creates a ransom note in _readme.txt file, which commands contacting cybercriminals via helpmanager@firemail.cc or helpmanager@iran.ir emails. The virus seeks to extort the victim and receive a ransom worth $490 or $980 in Bitcoin.
BTOS virus uses a strong file encryption algorithm to make data inaccessible to the victim. The point of encryption is to secure data so that only the particular individual could see it. To decrypt .btos file, a private decryption key is required, which is held by the cybercriminals. Unfortunately, it is inaccessible to the victims or cybersecurity researchers. Trying to crack it would take years, so it is out of the question.
The described STOP/DJVU variant enters the system alongside illegal online downloads and starts encrypting personal files right away. It must be noted that the ransomware encrypts the first 150KB of files, adding 334 bytes to the original file size due to usage of RSA-encrypted key, victim’s ID and filemarker. During the data corruption procedure, the virus leaves _readme.txt notes in each folder containing the files. Finally, the malware deletes system restore points which are often the victim’s last resort when it comes to data recovery.

What is even worse, BTOS virus tends to install password-stealing Trojans such as Azorult on the system. Therefore, if you have been attacked by this DJVU variant, consider all of your passwords stolen. You must eliminate the malware from your system and change your passwords then.
The best way to remove BTOS ransomware virus is in Safe Mode, so please jump to instructions provided below the article to accomplish this task.
Threat Summary
Name | BTOS ransomware virus |
Type | File-encrypting virus |
Origins | STOP/DJVU (202th version) |
Targeted systems | Windows |
Behavior | Encrypts files, restricts access to them and demands paying a ransom (according to instructions in _Readme.txt file) |
Extension | Appends .btos file extension to files |
Ransom note | _readme.txt |
Ransom demand | $490-$980 |
Emails | helpmanager@firemail.cc or helpmanager@iran.ir |
Distribution | Hides in illegal online downloads, such as KMSPico |
Decryption tools | STOP Decryptor doesn’t support this extension at the moment |
Removal | Remove using antivirus while in Safe Mode (see instructions below) |
Ransom demands stated in the note
BTOS file virus creates _readme.txt note to inform the victim about the cyberattack and state the further steps the victim must take if he/she wants to restore the data one day. According to the ransom note, all documents, databases and other files have been encrypted, and the only method to recover them is to pay the ransom.
The attackers suggest proving their abilities to recover data – the victim can send one small file for decryption. The further instructions on payment can be received by contacting the attackers via helpmanager@firemail.cc or helpmanager@iran.ir.
Data recovery is possible if encrypted with an offline key
During the data encryption, the described virus first attempts to establish a connection with its Command & Control server. Such a step is required to obtain individual ONLINE encryption keys for each victim. However, if the connection fails, the virus then uses a hardcoded OFFLINE encryption key to corrupt data.
The offline key is identical for all versions of BTOS extension virus. Once someone encrypted with offline key pays a ransom, the key then can be used by all victims of offline encryption. Therefore, we suggest you to keep checking for updates in this STOP/DJVU decryption guide.

You can check whether you’re subject to the offline encryption this way:
- Go to C:/SystemID/PersonalID.txt.
- Here, check the ending symbols of the ID or IDs stored here. If any of them ends in t1, it is an indicator of an offline encryption. All other cases mean online encryption.
DJVU distribution relies on illegal downloads
Computer users willing to avoid BTOS ransomware attack should stay away from illegal online downloads, including:
- Software cracks;
- Software license keygens;
- Illegal peer-to-peer downloads;
- Suspicious adware;
- Other shady files.
The STOP ransomware family variants such as TOPI, NOSU, REHA, or others are well-known to be included in malicious downloads such as KMSPico, so make sure you resist the temptation to install paid software for free. The risk of losing all of your data is very high.
Remove BTOS ransomware virus effectively
You must remove BTOS ransomware virus along with password-stealing Trojans it has installed on your computer. Successful elimination of the ransomware and its remains is essential when reacting to this type of cyberattack.
Following a BTOS virus removal, you should replace all of your passwords. Since the password-stealing Trojans tend to steal them from browser’s memory, try changing these passwords first. When it comes to .btos data recovery, check for your data backups, as this is the only way of restoring data corrupted by this virus variant now.
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BTOS Ransomware Removal Guidelines
Method 1. Enter Safe Mode with Networking
Step 1. Start Windows in Safe Mode with Networking
Before you try to remove the virus, you must start your computer in Safe Mode with Networking. Below, we provide the easiest ways to boot PC in the said mode, but you can find additional ones in this in-depth tutorial on our website – How to Start Windows in Safe Mode. Also, see a video tutorial on how to do it:
Instructions for Windows XP/Vista/7 users
- First of all, turn off your PC. Then press the Power button to start it again and instantly start pressing F8 button on your keyboard repeatedly in 1-second intervals. This launches the Advanced Boot Options menu.
- Use arrow keys on the keyboard to navigate down to Safe Mode with Networking option and press Enter.
Instructions for Windows 8/8.1/10 users
- Open Windows Start menu, then press down the Power button. On your keyboard, press down and hold the Shift key, and then select Restart option.
- This will take you to Windows Troubleshoot screen. Choose Troubleshoot > Advanced Options > Startup Settings > Restart. Tip: If you can't find Startup Settings, click See more recovery options.
- In Startup Settings, press the right key between F1-F9 to enter Safe Mode with Networking. In this case, it is the F5 key.
Step 2. Remove files associated with the virus
Now, you can search for and remove BTOS Ransomware files. It is very hard to identify files and registry keys that belong to the ransomware virus, Besides, malware creators tend to rename and change them repeatedly. Therefore, the easiest way to uninstall such type of a computer virus is to use a reliable malware removal program. In addition, we suggest trying a combination of INTEGO antivirus (removes malware and protects your PC in real-time) and RESTORO (repairs virus damage to Windows OS files).
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Scan your system for FREE to detect security, hardware and stability issues. You can use the scan results and try to remove threats manually, or you can choose to get the full version of software to fix detected issues and repair virus damage to Windows OS system files automatically. Includes Avira spyware/malware detection & removal engine.
Method 2. Use System Restore
In order to use System Restore, you must have a system restore point, created either manually or automatically.
Step 1. Boot Windows in Safe Mode with Command Prompt
Instructions for Windows XP/Vista/7 users
- Shut down your PC. Start it again by pressing the Power button and instantly start pressing F8 button on your keyboard repeatedly in 1-second intervals. You will see Advanced Boot Options menu.
- Using arrow keys on the keyboard, navigate down to Safe Mode with Command Prompt option and press Enter.
Instructions for Windows 8/8.1/10 users
- Launch Windows Start menu, then click the Power button. On your keyboard, press down and hold the Shift key, and then choose Restart option with the mouse cursor.
- This will take you to Windows Troubleshoot screen. Choose Troubleshoot > Advanced Options > Startup Settings > Restart. Tip: If you can't find Startup Settings, click See more recovery options.
- In Startup Settings, press the right key between F1-F9 to enter Safe Mode with Command Prompt. In this case, press F6 key.
Step 2. Start System Restore process
- Wait until system loads and command prompt shows up.
- Type cd restore and press Enter, then type rstrui.exe and press Enter. Or you can just type %systemroot%system32restorerstrui.exe in command prompt and hit Enter.
- This launches System Restore window. Click Next and then choose a System Restore point created in the past. Choose one that was created before ransomware infection.
- Click Yes to begin the system restoration process.
After restoring the system, we recommend scanning the system with antivirus or anti-malware software. In most cases, there won't be any malware remains, but it never hurts to double-check. In addition, we highly recommend checking ransomware prevention guidelines provided by our experts in order to protect your PC against similar viruses in the future.
Alternative software recommendations
Malwarebytes Anti-Malware
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Disclaimer. This site includes affiliate links. We may earn a small commission by recommending certain products, at no additional cost for you. We only choose quality software and services to recommend.

Norbert Webb is the head of Geek’s Advice team. He is the chief editor of the website who controls the quality of content published. The man also loves reading cybersecurity news, testing new software and sharing his insights on them. Norbert says that following his passion for information technology was one of the best decisions he has ever made. “I don’t feel like working while I’m doing something I love.” However, the geek has other interests, such as snowboarding and traveling.
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