22btc

[Content by Gemini 2.5]

The ransomware variant identified by the file extension .22btc is a component of a larger and very active ransomware family. While the extension itself is a specific identifier for this particular variant, it is widely recognized as one of the numerous extensions used by the STOP/DJVU ransomware family (also known as STOP Ransomware). Understanding this context is crucial, as many characteristics and recovery strategies apply to the broader STOP/DJVU family.

This document will provide a detailed technical breakdown and comprehensive recovery strategies for systems affected by the .22btc variant of STOP/DJVU ransomware.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The exact file extension appended to encrypted files by this variant is .22btc.
  • Renaming Convention: The ransomware encrypts files and appends the .22btc extension to the original filename.
    • Example: A file named document.docx would be renamed to document.docx.22btc.
    • Example: A file named photo.jpg would be renamed to photo.jpg.22btc.
      In addition to file encryption, the ransomware typically drops a ransom note named _readme.txt in every folder containing encrypted files and on the desktop. This note contains instructions for the victim on how to pay the ransom.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/DJVU ransomware family, which includes the .22btc variant, emerged around late 2018 or early 2019 and has remained one of the most prolific ransomware threats targeting individual users and small businesses globally. New variants with unique file extensions like .22btc are regularly released, often several times per week, making it a continuously evolving threat.

3. Primary Attack Vectors

The .22btc variant, like other STOP/DJVU strains, primarily relies on less sophisticated but highly effective propagation mechanisms, often targeting users with less stringent security practices.

  • Propagation Mechanisms:
    • Software Cracks and Pirated Content: This is the most common and significant vector. Users often download cracked software, illegal activators (keygens), pirated games, movies, or music from torrent sites or shady download portals. The ransomware is bundled within these seemingly innocuous downloads.
    • Fake Software Updates: Malicious websites or pop-ups may trick users into downloading what appears to be an urgent software update (e.g., for Flash Player, Java, web browsers) but is, in fact, the ransomware executable.
    • Malicious Advertisements (Malvertising): Compromised ad networks or rogue advertisers can display malicious ads that, when clicked or sometimes even just displayed, can lead to drive-by downloads or redirects to sites hosting the ransomware.
    • Email Phishing Campaigns: While less common than software cracks for STOP/DJVU, general ransomware distribution can occur via deceptive emails containing malicious attachments (e.g., seemingly legitimate invoices, shipping notifications, or resumes with embedded scripts or executables).
    • Fake Websites/Tech Support Scams: Users might be lured to malicious websites disguised as legitimate services or tech support, prompting them to download “tools” that are actually the ransomware.
    • Remote Desktop Protocol (RDP) Exploits: While not a primary vector for most STOP/DJVU infections (which target individual users), compromised RDP connections can be exploited by various ransomware groups to gain initial access to systems, especially in small business environments. However, for STOP/DJVU, direct user interaction with malicious downloads is far more prevalent.

Remediation & Recovery Strategies:

1. Prevention

Proactive measures are the most effective defense against ransomware like .22btc.

  • Regular Backups: Implement a robust 3-2-1 backup strategy (3 copies, on 2 different media, 1 offsite). Ensure backups are isolated (e.g., disconnected external drives, cloud backups with versioning) so they cannot be encrypted by ransomware.
  • Software Updates & Patching: Keep your operating system (Windows, macOS, Linux), web browsers, antivirus software, and all installed applications fully updated. Patches often fix security vulnerabilities that attackers could exploit.
  • Reputable Antivirus/Anti-Malware: Install and maintain a high-quality antivirus and anti-malware solution with real-time protection and behavioral analysis capabilities. Keep its definitions updated.
  • User Education: Educate users about the dangers of downloading pirated software, clicking suspicious links, opening unexpected email attachments, and visiting untrusted websites.
  • Network Security: Implement firewalls, disable unnecessary services (like SMBv1), and segment networks to limit lateral movement in case of an infection.
  • Strong Passwords & Multi-Factor Authentication (MFA): Use complex, unique passwords for all accounts and enable MFA wherever possible, especially for critical services and remote access.
  • Disable VSS Deletion (with caution): While STOP/DJVU attempts to delete Shadow Volume Copies, some tools can help prevent this or restore them if the ransomware fails. However, relying solely on VSS is not a substitute for proper backups.

2. Removal

If your system is infected, follow these steps for effective removal.

  • Isolate the Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet cable, disable Wi-Fi) to prevent the ransomware from spreading to other devices on the network.
  • Identify & Terminate Malicious Processes:
    1. Open Task Manager (Ctrl+Shift+Esc or Ctrl+Alt+Del -> Task Manager).
    2. Look for suspicious processes with unusual names or high CPU/memory usage. STOP/DJVU often uses random-looking executable names.
    3. End the process if identified, but be cautious as terminating critical system processes can cause instability.
  • Boot into Safe Mode: Restart the computer and boot into Safe Mode with Networking. This loads only essential services and drivers, making it easier to remove the ransomware without it actively encrypting or interfering.
  • Scan with Antivirus/Anti-Malware: Perform a full system scan using a reputable and updated antivirus/anti-malware program. Tools like Malwarebytes, ESET, or reputable enterprise-grade solutions are recommended. Allow the software to quarantine or remove detected threats.
  • Check Startup Items: Use Task Manager (Startup tab) or msconfig to disable any suspicious entries that attempt to launch the ransomware upon boot.
  • Remove Persistence Mechanisms:
    • Registry Entries: Check HKCU\Software\Microsoft\Windows\CurrentVersion\Run, HKLM\Software\Microsoft\Windows\CurrentVersion\Run, and similar locations for persistence.
    • Scheduled Tasks: Look for new or modified scheduled tasks that could re-launch the ransomware.
    • Hosts File Modification: STOP/DJVU often modifies the C:\Windows\System32\drivers\etc\hosts file to block access to security-related websites (like antivirus vendor sites or decryption tool sites). Open this file with Notepad and remove any suspicious entries, then save it.
  • Delete Ransom Note: Remove the _readme.txt files from all folders after the ransomware executable has been neutralized.

3. File Decryption & Recovery

The feasibility of decrypting files encrypted by .22btc (and other STOP/DJVU variants) depends heavily on whether an “online key” or “offline key” was used during encryption.

  • Recovery Feasibility:
    • Online Keys (Most Common): Most .22btc infections use an “online key.” This means a unique encryption key is generated on the attacker’s server for each victim. Without this specific key, which the attackers hold, decryption is currently impossible by third parties. Paying the ransom is strongly discouraged, as it funds cybercrime and offers no guarantee of decryption.
    • Offline Keys (Less Common): In some cases (e.g., if the victim’s internet connection was unstable during the infection, or the ransomware couldn’t reach its C2 server), an “offline key” might be used. These keys are hardcoded into the ransomware or derived locally. If an offline key was used, there is a chance that a publicly available decryptor might work.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP/DJVU: Emsisoft, in collaboration with the security community, has developed a free decryptor for STOP/DJVU ransomware. This tool is the only legitimate third-party decryptor available.
      • How it works: The Emsisoft decryptor attempts to match fragments of encrypted files with known encryption patterns (derived from offline keys or previously compromised online keys). If it finds a match, it can decrypt files.
      • Limitations: It primarily works for offline keys and for online keys that have been previously obtained or cracked. For new online key infections, it will likely indicate that decryption is “impossible” or that an unknown key was used.
    • File Recovery Software: If Shadow Volume Copies were not deleted (unlikely with STOP/DJVU, which actively deletes them), tools like PhotoRec, Recuva, or Disk Drill might be able to recover older, unencrypted versions of files. However, this is rarely successful against modern ransomware that specifically targets and deletes VSS.
    • Backups: The most reliable method for recovery is to restore from clean, uninfected backups created before the infection.

4. Other Critical Information

  • Unique Characteristics:
    • Online vs. Offline Keys: This is the most distinguishing feature impacting recovery. Victims can often check their _readme.txt note; if it refers to personalid.txt and contains an ID that starts with a set pattern (e.g., sfgd or t1t followed by many characters), it might indicate an online key.
    • _readme.txt Ransom Note: The consistent use of this specific filename for the ransom note across all STOP/DJVU variants.
    • Hosts File Modification: The ransomware’s attempt to block access to security research sites and forums by modifying the hosts file to prevent victims from seeking help.
    • Shadow Copy Deletion: Aggressive deletion of Volume Shadow Copies (VSS) to prevent easy recovery from built-in Windows restore points.
  • Broader Impact:
    • High Volume Threat: STOP/DJVU (and thus .22btc) is one of the most widespread ransomware families, primarily because its attack vectors (pirated software) are so common among a large user base.
    • Individual & Small Business Focus: While not typically targeting large enterprises, its sheer volume means it significantly impacts individuals, students, home users, and small businesses who often lack sophisticated security measures.
    • Economic Impact: Even with relatively small ransom demands (typically $490-$980 in Bitcoin), the cumulative economic impact of lost data and recovery efforts is substantial due to the high number of victims.
    • Psychological Distress: The loss of irreplaceable personal files (photos, documents) causes significant distress, especially when no decryption is possible without paying the ransom.

In conclusion, while the .22btc ransomware variant is a persistent threat, understanding its technical underpinnings and adhering to robust prevention and recovery strategies, particularly through the use of isolated backups, is paramount to mitigating its impact. Paying the ransom should always be the last resort and is generally not recommended.