*[email protected]*

[Content by Gemini 2.5]

This detailed resource is designed to equip individuals and organizations with the necessary knowledge and strategies to combat the ransomware variant identified by the file extension *[email protected]*. This particular variant is part of the prolific STOP/Djvu ransomware family, which has seen continuous evolution and widespread distribution.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by this variant will have the .{random_string}[email protected] extension appended to their original filenames. The “random string” is typically 4-7 characters long.
  • Renaming Convention: The ransomware follows a clear pattern:
    1. The original filename remains intact.
    2. A unique, randomly generated alphanumeric string (usually 4-7 characters) is inserted before the primary ransomware extension.
    3. The final, consistent ransomware extension [email protected] is appended.
      Alongside file encryption, the ransomware typically drops a ransom note named _readme.txt in every folder containing encrypted files, providing instructions for victims to contact the attackers.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family emerged in late 2017/early 2018 and has been continuously active and evolving since then. The *[email protected]* variant represents one of the many extensions consistently deployed by this group as part of their ongoing campaign. While a precise “start date” for this specific extension is difficult to pinpoint, it follows a pattern of new extensions being released frequently, indicating continuous updates and propagation within the broader STOP/Djvu operation, likely appearing in recent months as of this document’s creation.

3. Primary Attack Vectors

*[email protected]*, like other STOP/Djvu variants, primarily leverages methods that target individual users rather than large enterprise networks, though lateral movement within an organization is possible post-initial compromise.

  • Propagation Mechanisms:
    • Cracked Software & Illegitimate Downloads: This is the most prevalent method. Users download pirated software, key generators (keygens), software cracks, installers for popular applications (e.g., Photoshop, Microsoft Office), or games from untrusted sources (e.g., torrent sites, warez forums, free download sites). The ransomware is bundled within these seemingly legitimate installers.
    • Fake Updates & Malvertising: Malicious advertisements or pop-ups prompting users to install “critical updates” for web browsers, Flash Player, or other common software often contain the ransomware payload.
    • Phishing Campaigns (Malspam): While less common for the initial infection compared to the methods above, email attachments (e.g., seemingly legitimate invoices, shipping notifications, or resumes) containing malicious scripts or documents can deliver the ransomware.
    • Compromised Websites: Visiting compromised websites that automatically download malware (drive-by downloads) or trick users into executing malicious files can also lead to infection.
    • Remote Desktop Protocol (RDP) Exploits: While not a primary initial infection vector for STOP/Djvu, weak or exposed RDP credentials can be exploited to gain access to a system, after which the ransomware could be manually deployed.
    • Software Vulnerabilities: Less frequently, unpatched vulnerabilities in common applications or operating systems might be exploited, though this is not a hallmark of STOP/Djvu’s typical propagation.

Remediation & Recovery Strategies:

1. Prevention

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

  • Regular Backups (Offline/3-2-1 Rule): Implement a robust backup strategy. Store critical data on external drives, network-attached storage (NAS) disconnected from the network, or cloud services with versioning. Follow the 3-2-1 rule: 3 copies of your data, on 2 different media, with 1 copy off-site/offline.
  • Software Updates & Patching: Keep your operating system, applications (especially web browsers, antivirus, and common utilities), and firmware fully updated. Enable automatic updates where feasible.
  • Reputable Antivirus/Endpoint Detection & Response (EDR): Install and maintain a high-quality antivirus or EDR solution with real-time protection and behavioral analysis capabilities. Ensure its definitions are regularly updated.
  • Email Security & User Awareness Training: Implement email filtering to block malicious attachments and links. Educate users about phishing, social engineering tactics, and the dangers of clicking suspicious links or opening unsolicited attachments.
  • Strong Passwords & Multi-Factor Authentication (MFA): Use strong, unique passwords for all accounts. Enable MFA wherever possible, especially for critical systems and cloud services.
  • Disable Macros by Default: Configure Microsoft Office and other productivity suites to disable macros by default, or only enable them for trusted documents.
  • Network Segmentation: For organizations, segment your network to limit the lateral movement of ransomware if an infection occurs.
  • Restrict User Privileges: Follow the principle of least privilege, granting users only the necessary permissions to perform their tasks.

2. Removal

If a system is infected, follow these steps to remove *[email protected]*:

  1. Isolate the Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet cable, disable Wi-Fi). This prevents the ransomware from spreading to other devices or network shares.
  2. Identify and Scan: Use a reputable antivirus or anti-malware scanner to perform a full system scan. It’s often advisable to do this in Windows Safe Mode with Networking to prevent the ransomware from interfering with the scanning process.
    • Recommended Tools: Malwarebytes, SpyHunter, Zemana Anti-Malware, or your existing trusted AV.
  3. Remove Malicious Files: Allow the security software to quarantine and remove all detected threats, including the ransomware executable, associated dropped files, and any persistence mechanisms.
  4. Check for Persistence Mechanisms:
    • Registry Entries: Scan and remove any suspicious entries in HKCU\Software\Microsoft\Windows\CurrentVersion\Run or HKLM\Software\Microsoft\Windows\CurrentVersion\Run that launch the ransomware.
    • Scheduled Tasks: Check Task Scheduler for any newly created tasks designed to re-launch the ransomware.
    • Startup Folders: Examine shell:startup and shell:common startup for suspicious shortcuts or executables.
  5. Clean up hosts file: STOP/Djvu variants often modify the C:\Windows\System32\drivers\etc\hosts file to block access to security-related websites. Remove any entries related to anti-malware sites.
  6. Change Passwords: Once the system is clean, change all passwords used on or accessible from the infected system, especially those for online services and network shares.
  7. Monitor: Continue to monitor the system for any signs of re-infection or suspicious activity.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Decryption for *[email protected]* (STOP/Djvu): The feasibility of decrypting files encrypted by STOP/Djvu variants, including *[email protected]*, largely depends on the encryption key used:
      • Online Keys (Most Common): If the victim’s computer had an active internet connection during encryption, the ransomware generates a unique “online key” specific to that victim and sends it to the attackers’ server. In this scenario, decryption without the attackers’ private key is currently impossible. No universal decryptor exists for files encrypted with online keys.
      • Offline Keys (Rare/Fortuitous): If the victim’s computer did not have an active internet connection during encryption, the ransomware falls back to using a hardcoded “offline key.” While this key is unique to a specific variant (e.g., *[email protected]*), it is the same for all victims encrypted with that variant offline. Reputable cybersecurity firms like Emsisoft have developed decryptors for many STOP/Djvu offline keys as they are discovered and shared by researchers or victims.
    • Shadow Volume Copies: STOP/Djvu typically deletes Shadow Volume Copies using vssadmin.exe delete shadows /all /quiet to prevent easy recovery.
    • Data Recovery Software: In some cases, if the original files were not fully overwritten but merely encrypted and then deleted (leaving the encrypted copy), data recovery software (e.g., PhotoRec, Recuva) might be able to recover older, unencrypted versions of files. Success rates vary widely.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP Djvu: This is the primary tool for potential decryption. Victims can submit encrypted files to Emsisoft’s tool. It attempts to identify if an offline key was used and if a decryptor for that key is available. Keep in mind, this tool will not work for files encrypted with online keys.
    • System Restore Points: While often deleted by the ransomware, if you have recent System Restore Points created before the infection, they might help restore system files, but typically not personal data.
    • Backup Solutions: As mentioned in prevention, a reliable backup solution is the most effective recovery tool. Restore your data from backups created prior to the infection.

4. Other Critical Information

  • Additional Precautions – Information Stealers: A significant and dangerous characteristic of recent STOP/Djvu variants (including *[email protected]*) is that they often bundle and install additional malware, most commonly information stealers like Vidar Stealer, RedLine Stealer, or Racoon Stealer. These stealers harvest a wide range of sensitive data from the infected system, including:
    • Browser saved passwords, cookies, credit card details.
    • Cryptocurrency wallet data.
    • Two-factor authentication codes.
    • VPN credentials.
    • Screenshot of desktop.
    • System information.
      This means even if you manage to remove the ransomware and recover some files, your personal information may already have been compromised and sold on dark web markets. It is crucial to assume that all your online accounts are compromised and change passwords immediately from a clean system.
  • Broader Impact:
    • Data Loss: For victims encrypted with online keys, data loss is highly probable if no backups exist and paying the ransom is not an option (or not successful).
    • Financial Cost: Victims face the potential cost of paying the ransom (which is never guaranteed to result in decryption), significant IT recovery costs, and potential legal/regulatory fines if sensitive data was exfiltrated.
    • Operational Disruption: For businesses, infection leads to downtime, lost productivity, and potential reputational damage.
    • Identity Theft & Fraud: Due to the common bundling with information stealers, victims are at high risk of identity theft, financial fraud, and account compromise.
    • Perpetual Threat: The continuous release of new STOP/Djvu extensions highlights the persistent nature of this threat, requiring ongoing vigilance and robust cybersecurity practices.

By understanding these technical details and implementing the recommended recovery strategies, individuals and organizations can significantly improve their resilience against *[email protected]* and other variants of the STOP/Djvu ransomware.