*.*[email protected]*.angus

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This document provides a detailed technical breakdown and comprehensive recovery strategies for the ransomware variant identified by the file extension *.*[email protected]*.angus.

Technical Breakdown:

This ransomware variant is a member of the STOP/Djvu ransomware family, one of the most prolific and continuously evolving ransomware strains active today. The string *.*[email protected]*.angus indicates the characteristic renaming pattern and the specific variant identifier.

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by this variant will typically have a new extension appended to their original filename. Based on the provided identifier, the most common pattern for STOP/Djvu variants is .<ID>.<variant_extension>. Therefore, a file named document.docx might become document.docx.<4-random-chars>.angus. The [email protected] component is not usually part of the appended file extension itself but rather the contact email address provided to the victim in the ransom note.
    • Example Renaming: myphoto.jpg might be renamed to myphoto.jpg.asfd.angus (where asfd is a unique 4-character ID).
  • Renaming Convention: The ransomware appends a unique victim ID (a string of characters) followed by the specific variant extension (.angus in this case) to the original filename. For instance, original_file.txt would become original_file.txt.[unique_ID].angus. A ransom note, typically named _readme.txt, is dropped in every folder containing encrypted files and on the desktop. This note contains instructions for the victim, including the contact email (likely [email protected] or similar) and the ransom demand.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family has been active since late 2017/early 2018. New variants, like “angus,” are released regularly, sometimes daily or weekly, by the ransomware operators. This particular “angus” variant would have emerged as part of this ongoing release cycle, likely in late 2023 or early 2024, given the continuous nature of Djvu’s evolution. It continues to be actively distributed.

3. Primary Attack Vectors

*.*[email protected]*.angus (as a STOP/Djvu variant) primarily propagates through deceptive methods targeting individual users and small businesses rather than large enterprises or critical infrastructure via sophisticated exploits.

  • Propagation Mechanisms:
    1. Bundled Software/Cracked Software: This is the most prevalent infection vector. The ransomware is frequently distributed as part of software cracks, key generators, pirated software installers (e.g., for popular games, Adobe products, Microsoft Office), and unofficial installers downloaded from dubious websites. Users seeking free software often unknowingly download and execute the ransomware alongside the desired application.
    2. Malicious Websites and Downloads: Drive-by downloads from compromised websites, fake software update pages, or malicious advertisements can also lead to infection.
    3. Phishing Campaigns (Less Common for Djvu, but possible): While less common than software bundling, phishing emails containing malicious attachments (e.g., seemingly legitimate documents with embedded macros) or links to malware download sites can also be used.
    4. Infected USB Drives/External Media: Although less frequent now, the ransomware could spread if an infected removable drive is connected to a clean system, especially if autorun is enabled.

Remediation & Recovery Strategies:

1. Prevention

Proactive measures are the most effective defense against ransomware like *.*[email protected]*.angus.

  • Proactive Measures:
    1. Regular Data Backups: Implement a robust 3-2-1 backup strategy: at least three copies of your data, stored on two different media types, with one copy offsite or offline (e.g., cloud storage, external hard drive disconnected after backup). Test your backups regularly.
    2. Use Legitimate Software: Only download software, games, and media from official, reputable sources. Avoid software cracks, keygens, torrent sites, and unofficial download portals.
    3. Endpoint Protection: Deploy and maintain a reputable antivirus/anti-malware solution with real-time protection and behavioral analysis capabilities. Ensure it is always updated.
    4. Operating System & Software Updates: Keep your operating system, web browsers, and all installed applications fully patched and updated. This closes security vulnerabilities that ransomware might exploit.
    5. Network Segmentation: For organizations, segmenting your network can limit the lateral movement of ransomware if an infection occurs.
    6. Strong Passwords & MFA: Use strong, unique passwords for all accounts, especially for remote access services. Enable Multi-Factor Authentication (MFA) wherever possible.
    7. Email Security & User Training: Implement email filtering to block malicious attachments and links. Educate users about phishing scams and the dangers of opening suspicious attachments or clicking unknown links.
    8. Disable RDP if Not Needed: If Remote Desktop Protocol (RDP) is not essential, disable it. If required, secure it with strong passwords, MFA, and network-level authentication (NLA), and restrict access to trusted IPs.
    9. Disable Shadow Copies (Backup Strategy): While ransomware often deletes shadow copies, having them enabled (and protected) as a temporary measure can sometimes aid recovery for some file types if the ransomware fails to delete them. However, relying on them as a primary backup is not recommended.

2. Removal

Removing the ransomware executable is a critical first step but does not decrypt files.

  • Infection Cleanup:
    1. Isolate the Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet cable, turn off Wi-Fi). This prevents further spread to other devices on the network.
    2. Identify and Terminate Processes: Use Task Manager (Windows) to look for suspicious processes. However, identifying the ransomware executable can be difficult as it often mimics legitimate process names or self-deletes/changes names after encryption.
    3. Boot into Safe Mode: Restart the computer in Safe Mode with Networking. This often prevents the ransomware from fully loading.
    4. Run Full System Scans: Use multiple reputable anti-malware tools (e.g., Malwarebytes, Windows Defender, HitmanPro) to perform thorough full-system scans. These tools are often updated to detect and remove known ransomware executables and associated malicious files.
    5. Check Startup Entries and Scheduled Tasks: Use tools like Autoruns or Msconfig to check for suspicious entries that allow the ransomware to persist across reboots and remove them.
    6. Clean Hosts File: STOP/Djvu ransomware often modifies the hosts file (C:\Windows\System32\drivers\etc\hosts) to block access to security-related websites (e.g., antivirus vendors). Check and restore the hosts file to its default state.
    7. Remove Ransom Note: Delete the _readme.txt files from all affected directories and the desktop after you have saved a copy for incident response purposes.

3. File Decryption & Recovery

  • Recovery Feasibility: The possibility of decrypting files encrypted by *.*[email protected]*.angus without paying the ransom is limited but not impossible, primarily depending on whether an “online key” or “offline key” was used during encryption.
    • Online Keys (Most Common): The vast majority of recent STOP/Djvu infections use unique online encryption keys generated specifically for each victim. For these cases, there is currently no free decryption tool available. The only way to decrypt files is to obtain the private key from the attackers (by paying the ransom, which is strongly discouraged due to no guarantee of decryption and funding criminal activity) or for security researchers to find a fundamental flaw in the encryption scheme, which is rare.
    • Offline Keys (Rare): In some rare instances (e.g., if the ransomware cannot connect to its command-and-control server), an “offline key” might be used. Files encrypted with offline keys can sometimes be decrypted by tools like the Emsisoft STOP/Djvu Decryptor. This tool uses a database of known offline keys. You will need to submit an encrypted file and its original (unencrypted) counterpart to the Emsisoft service for analysis to determine if an offline key match exists.
  • Essential Tools/Patches:
    • Emsisoft STOP/Djvu Decryptor: This is the primary tool to attempt free decryption for files encrypted by offline keys. It’s crucial to understand its limitations for online key cases.
    • Reputable Anti-Malware Software: (e.g., Malwarebytes, Windows Defender, AVG, Avast, Sophos, ESET). Use for removing the ransomware itself.
    • Data Recovery Software: Tools like PhotoRec or Recuva might be able to recover older, unencrypted versions of files or shadow copies if they were not completely deleted by the ransomware. However, success rates are often low for heavily encrypted systems.
    • Windows System Restore / Previous Versions: If System Restore points or Previous Versions were active and not deleted by the ransomware, you might be able to restore older versions of files or the entire system state. ransomware often attempts to delete these, so success is not guaranteed.

4. Other Critical Information

  • Additional Precautions (Unique Characteristics of STOP/Djvu):
    1. Hosts File Modification: As mentioned, STOP/Djvu commonly modifies the hosts file to block access to security-related websites, hindering victims from seeking help or downloading security tools.
    2. Shadow Copy Deletion: It typically uses vssadmin.exe Delete Shadows commands to eliminate Volume Shadow Copies, making recovery via Windows built-in features difficult.
    3. Information Stealers: Newer variants of STOP/Djvu are frequently bundled with information-stealing malware (e.g., Vidar Stealer, RedLine Stealer, Raccoon Stealer). This means that beyond file encryption, your sensitive data (browser passwords, cryptocurrency wallet details, banking information, cookies, etc.) might also have been exfiltrated. This necessitates immediate password changes for all online accounts from a clean, uninfected device, and monitoring financial accounts for suspicious activity.
    4. Fake Error Messages: The ransomware might display fake error messages (e.g., related to Windows updates or software installations) to mislead victims about the cause of system issues.
  • Broader Impact: The “angus” variant, like other STOP/Djvu strains, primarily impacts individual users and small businesses. Its widespread distribution via pirated software leads to:
    • Significant Data Loss: If backups are not available or are also encrypted.
    • Financial Costs: Through ransom demands (if paid) or the cost of recovery efforts.
    • Operational Disruption: For businesses, losing access to critical files can halt operations.
    • Privacy Compromise: Due to potential information-stealing modules, leading to further risks like identity theft or financial fraud.
    • Psychological Distress: For individuals who lose irreplaceable personal photos, documents, or projects.

In conclusion, while direct decryption for *.*[email protected]*.angus (and most STOP/Djvu variants) is often not feasible without paying the ransom, robust prevention, diligent removal, and a comprehensive backup strategy remain the most effective defenses against this pervasive threat.