*[email protected]*

[Content by Gemini 2.5]

This document provides a comprehensive overview of the ransomware variant identified by the file extension containing *[email protected]*. This specific identifier is commonly associated with variants of the STOP/Djvu ransomware family, one of the most prolific and continuously evolving ransomware threats. While the exact file extension can vary slightly between sub-variants, the [email protected] string typically serves as the primary contact email for the attackers and a unique marker for the specific variant.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    Files encrypted by this ransomware variant will have an additional extension appended to their original filename. This new extension will typically include or directly be [email protected]. For example, a file named document.docx might be renamed to document.docx.[random_characters][email protected] or [email protected]. The exact format often involves a unique identifier string (e.g., 4 random characters or a specific variant ID) prepended to the [email protected] string.

  • Renaming Convention:
    The general renaming convention follows the pattern:
    [original_filename].[original_extension].[unique_variant_ID].[contact_email_extension]
    Or
    [original_filename].[original_extension].[contact_email_extension]
    Where [contact_email_extension] is typically [email protected] or a variant of it. The original file content is encrypted and then replaced with the encrypted version, identifiable by this new, appended extension.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    The STOP/Djvu ransomware family, to which [email protected] variants belong, emerged in late 2018 and has maintained a high level of activity since. New variants are constantly being released. Specific variants using the [email protected] contact method have been observed in circulation over different periods, indicating its continued use as a communication channel by the ransomware operators. Its broad activity has spanned from 2019 onwards, adapting and evolving with new obfuscation techniques and attack vectors.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    STOP/Djvu ransomware, including variants using [email protected], primarily relies on social engineering and deceptive distribution methods rather than exploiting network vulnerabilities for rapid self-propagation. Common attack vectors include:
    • Cracked Software/Pirated Content: The most prevalent method involves embedding the ransomware within installers for cracked software, pirated games, key generators, and illicit activators downloaded from torrent sites or untrustworthy file-sharing platforms.
    • Fake Software Updates: Malicious websites or pop-ups may trick users into downloading what appears to be a legitimate software update (e.g., Flash Player, Java), but which secretly contains the ransomware payload.
    • Malvertising: Malicious advertisements on legitimate or compromised websites can redirect users to landing pages that automatically download the ransomware or prompt them to download a fake update.
    • Phishing Campaigns: While less common than cracked software for Djvu, some variants can be spread via deceptive emails containing malicious attachments (e.g., seemingly legitimate documents with embedded macros) or links to compromised websites.
    • Unsecured Remote Desktop Protocol (RDP): In some cases, weak or exposed RDP configurations can be exploited to gain initial access to a system, though this is less typical for broad Djvu campaigns compared to other ransomware families.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Regular Backups: Implement a robust 3-2-1 backup strategy (3 copies of data, 2 different media types, 1 offsite). Ensure backups are immutable or stored offline/air-gapped to prevent them from being encrypted.
    • Antivirus/Anti-Malware Software: Install and maintain reputable endpoint protection (antivirus/anti-malware) software with real-time protection and behavior-based detection enabled. Keep signatures updated.
    • Software Updates & Patching: Regularly update your operating system (Windows, macOS, Linux) and all installed software. This is crucial for patching known vulnerabilities that could be exploited.
    • Email Filtering & Security: Utilize email security solutions to filter out malicious attachments and suspicious links. Educate users about identifying phishing attempts.
    • User Account Control (UAC) & Least Privilege: Run with standard user accounts whenever possible and use administrator privileges only when necessary.
    • Network Segmentation: Isolate critical systems and data on separate network segments to limit lateral movement in case of an infection.
    • Disable Unnecessary Services: Turn off services like SMBv1, RDP (if not needed), or ensure they are securely configured with strong passwords and multi-factor authentication (MFA).

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.
    2. Identify and Terminate Ransomware Processes: Boot into Safe Mode with Networking (if possible) or use a rescue environment. Use Task Manager or a process explorer tool (e.g., Process Explorer) to identify and terminate suspicious processes. Look for newly created processes with unusual names.
    3. Scan and Remove Malware: Perform a full system scan using a reputable and updated antivirus/anti-malware suite. Tools like Malwarebytes, Kaspersky Virus Removal Tool, or ESET Online Scanner can be effective.
    4. Clean Up Malicious Files: Delete all identified malicious files, including the ransomware executable, any dropper files, and associated components. Check common locations like AppData, ProgramData, Temp folders, and Startup directories.
    5. Remove Persistence Mechanisms: Check and remove any persistence mechanisms the ransomware might have established (e.g., registry run keys, scheduled tasks, startup folder entries).
    6. Check 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 vendor sites, forums offering help). Review this file and remove any suspicious entries.
    7. Change All Passwords: After confirming the system is clean, change all passwords, especially for online services, email, and network shares that were accessible from the infected machine.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Decryption of files encrypted by [email protected] variants of STOP/Djvu ransomware is challenging and often not possible without the unique decryption key.

    • Online Keys: Most modern Djvu variants use “online keys” (unique keys generated for each victim and transmitted to the command-and-control server). Without this specific key, which the attackers hold, decryption is generally impossible.
    • Offline Keys: In rare cases, if the ransomware failed to connect to its C2 server, it might use a pre-set “offline key.” If this occurs, there’s a slim chance that a universal decryptor might work.
    • Emsisoft Decryptor: Emsisoft, in collaboration with Michael Gillespie (MalwareHunterTeam), maintains a decryptor for STOP/Djvu ransomware. This tool is constantly updated to support new offline key variants. It is the primary legitimate tool to attempt decryption. However, it will not work for online key variants unless the specific online key is somehow obtained or released.
    • Paying the Ransom: Paying the ransom is strongly discouraged. There is no guarantee that the attackers will provide a working decryption key, and it funds future criminal activities.

  • Essential Tools/Patches:

    • Emsisoft Decryptor for STOP/Djvu: The most important tool for potential decryption (download from Emsisoft’s official website).
    • Reputable Antivirus/Anti-Malware Software: For removal and prevention (e.g., Malwarebytes, Bitdefender, Kaspersky).
    • Data Recovery Software: Tools like Shadow Explorer or Recuva might help recover unencrypted copies if Shadow Volume Copies were not deleted by the ransomware (Djvu often attempts to delete them).
    • Windows System Restore/File History: If enabled, these features might allow you to revert your system or recover files from a point before encryption.
    • Operating System Patches: Ensure Windows is fully updated to mitigate potential vulnerabilities.

4. Other Critical Information

  • Additional Precautions:

    • Ransom Note: The ransomware typically drops a ransom note named _readme.txt in every folder containing encrypted files, and often on the desktop. This note contains instructions for payment and contact details ([email protected]).
    • Shadow Volume Copies Deletion: [email protected] variants, like other Djvu strains, are known to delete Shadow Volume Copies (using vssadmin.exe delete shadows /all /quiet) to prevent easy file recovery.
    • hosts File Modification: They commonly modify the hosts file to block access to security-related websites, making it harder for victims to seek help or download removal tools.
    • System Slowdown: Victims may notice a slowdown in system performance during the encryption process.

  • Broader Impact:
    The STOP/Djvu family, including the [email protected] variants, has a significant broader impact, primarily targeting individual users and small businesses rather than large enterprises. Its ease of distribution via cracked software and high volume of attacks make it one of the most common ransomware infections. While the ransom demands are typically lower than those of major enterprise-targeting ransomware, the sheer number of victims contributes to substantial financial losses globally. Its continuous evolution poses an ongoing challenge for cybersecurity researchers and users alike, as new variants with slightly modified code and changing extensions/contact methods appear regularly.