*[email protected]*

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This document provides a comprehensive overview of the ransomware variant associated with the file extension *[email protected]*. Based on the distinct file extension pattern, this variant is identified as part of the prolific STOP/Djvu ransomware family. These variants are known for appending the attacker’s contact email (or a unique ID followed by the email) to encrypted files.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The exact file extension used by this ransomware is typically a combination of a unique victim ID and the attacker’s contact email. For files encrypted by this specific variant, the appended string will be .[unique_ID][email protected] or simply [email protected].
  • Renaming Convention: When a file, for example, document.docx, is encrypted, it will be renamed to something like document.docx.[unique_ID][email protected]. The [unique_ID] is a string of alphanumeric characters generated for each victim. In some cases, older or specific variants might just append [email protected] directly.
  • Ransom Note: A ransom note, typically named _readme.txt, is dropped in every folder containing encrypted files. This note instructs the victim on how to contact the attackers via the specified email address ([email protected]) for decryption instructions.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family, to which this variant belongs, has been highly active since late 2018 and continues to evolve with new variants emerging regularly. Variants using specific email addresses like [email protected] appear as part of this ongoing evolution. Its peak activity periods have been consistent, making it one of the most widespread consumer-level ransomware threats.

3. Primary Attack Vectors

  • Propagation Mechanisms: STOP/Djvu ransomware, including the [email protected] variant, primarily relies on social engineering tactics and less on sophisticated network exploitation. Common propagation methods include:
    • Bundled Software/Cracked Software: This is the most prevalent method. Users often download pirated software, “cracked” applications, key generators, or activators from torrent sites or untrusted download portals. The ransomware is bundled within these executables, installing silently alongside the desired (but illegitimate) software.
    • Fake Software Updates: Malicious websites or pop-ups may prompt users to download fake updates for legitimate software (e.g., Flash Player, Java, web browsers), which are actually trojanized installers containing the ransomware.
    • Phishing Campaigns: While less common than software bundling, targeted phishing emails containing malicious attachments (e.g., seemingly legitimate documents with embedded macros) or links to infected websites can also be used.
    • Malicious Advertisements (Malvertising): Compromised ad networks or websites serving malicious advertisements can redirect users to exploit kits or directly download the ransomware.
    • Remote Desktop Protocol (RDP) Exploits: While not a primary vector for mass distribution of STOP/Djvu, poorly secured RDP connections can be exploited by attackers to manually deploy the ransomware onto a victim’s network.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    1. Regular 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., external hard drive disconnected after backup, cloud storage). This is the most crucial defense.
    2. Software Legality: Avoid downloading or installing cracked software, keygens, or activators from unofficial sources. These are prime distribution channels for STOP/Djvu.
    3. Software & OS Updates: Keep your operating system, applications, and antivirus software up to date with the latest security patches.
    4. Strong Endpoint Security: Use a reputable antivirus/anti-malware suite with real-time protection and behavioral detection capabilities. Ensure it’s always active and updated.
    5. Email Security Awareness: Be extremely cautious with unsolicited emails. Never open attachments or click links from unknown senders. Verify sender identity before interacting with suspicious emails.
    6. Ad Blocker/Script Blocker: Use browser extensions to block malicious ads and scripts that could lead to drive-by downloads.
    7. Disable AutoPlay: Disable the AutoPlay feature for removable media to prevent automatic execution of malware.
    8. Least Privilege Principle: Run your daily computing activities with a standard user account, not an administrator account. Only use admin privileges when absolutely necessary.

2. Removal

  • Infection Cleanup:
    1. Isolate the Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet cable, disable Wi-Fi) to prevent further spread to other devices on the local network.
    2. Identify and Quarantine: Use a reputable antivirus or anti-malware solution (e.g., Malwarebytes, ESET, Bitdefender, SpyHunter) to perform a full system scan. The ransomware executable itself needs to be identified and quarantined/deleted.
    3. Remove Persistent Elements: STOP/Djvu often creates scheduled tasks, modifies registry entries, and drops copies of itself in various system folders (e.g., AppData\Local, ProgramData). Advanced anti-malware tools should detect and remove these. Manual removal is highly risky and not recommended without expert knowledge.
    4. Check for Information Stealers: Crucially, STOP/Djvu variants often drop additional malware, such as information stealers (e.g., Vidar, Azorult, RedLine), which can steal passwords, cryptocurrency wallets, browser data, and other sensitive information. After removing the ransomware, perform a deep scan for these threats and change all critical passwords (email, banking, social media, etc.) from a clean device.
    5. System Restore Point Deletion: The ransomware typically attempts to delete Volume Shadow Copies to prevent easy recovery.

3. File Decryption & Recovery

  • Recovery Feasibility: Decryption of files encrypted by STOP/Djvu variants, including [email protected], is complex and often depends on the type of encryption key used:
    • Online Key (Most Common): If the victim’s system had an active internet connection during encryption, the ransomware generates a unique “online” encryption key, which is then uploaded to the attackers’ server. In this scenario, decryption without the attackers’ key is generally not possible. Paying the ransom is strongly discouraged as there’s no guarantee of decryption, and it fuels future attacks.
    • Offline Key (Less Common): If the system was offline during encryption (or the connection to the C2 server failed), the ransomware falls back to a limited set of “offline” keys. For these cases, security researchers (notably Emsisoft and Michael Gillespie) have developed a free decryptor for STOP/Djvu.
      • How to check: The ransom note will usually contain a personal ID. If the last few characters of the ID are t1, t3, or similar, it might indicate an offline ID.
      • Tools: The Emsisoft Decryptor for STOP/Djvu Ransomware is the primary tool for attempts at recovery.
      • Requirements for Decryption (Offline Keys): The decryptor often requires an encrypted file and its original, unencrypted version (if available) to analyze the encryption pattern. It also needs the PersonalID from the ransom note. If possible, providing the original malware executable can also assist in analysis.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP/Djvu: The go-to tool for potential offline key decryption.
    • Reputable Antivirus/Anti-malware: For removal of the ransomware executable and associated malware.
    • System Patches: Keep Windows and all software updated.
    • Backup Solutions: Critical for true recovery.

4. Other Critical Information

  • Additional Precautions:
    • Information Stealer Risk: The most significant unique characteristic of STOP/Djvu (and thus [email protected] variant) is its consistent deployment of information-stealing malware alongside the ransomware. This means even if you don’t pay the ransom and manage to clean your system, your sensitive data (passwords, cryptocurrency, browser history, etc.) might already be compromised. Immediately change all critical passwords from a clean device after detecting an infection.
    • Shadow Copy Deletion: This ransomware aggressively deletes Volume Shadow Copies, making it harder to recover files using native Windows features.
    • Fake Decryptors: Be extremely wary of “decryption services” or “decryptors” offered by untrusted sources. Many are scams, or worse, contain additional malware. Stick to tools provided by reputable cybersecurity firms.
  • Broader Impact:
    • Widespread Consumer Impact: STOP/Djvu and its variants like [email protected] have disproportionately affected individual users and small businesses due to their distribution methods (pirated software).
    • Financial Loss: Victims face not only potential data loss but also financial demands (ransom payments, data recovery services) and the cost of replacing compromised systems or lost productivity.
    • Identity Theft Risk: The simultaneous deployment of info-stealers means victims are at higher risk of identity theft, financial fraud, and account compromise, even if file decryption is not their primary concern. This necessitates a thorough post-infection cleanup and password reset strategy.

By understanding the technical nuances and implementing the recommended recovery strategies, individuals and organizations can better defend against and respond to the *[email protected]* ransomware variant.