*[email protected]*

[Content by Gemini 2.5]

The file extension *[email protected]* is a strong indicator of a variant belonging to the STOP/Djvu ransomware family. This family is one of the most prolific and continuously evolving threats targeting individuals and small businesses. The email address within the extension typically serves as a unique identifier for the specific variant or the contact method for the attackers.

Here’s a detailed breakdown of this ransomware variant:

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by this variant will typically have a double extension appended to their original name. The full pattern is .[original_4_char_extension][email protected]. For instance, if the variant uses a base extension like .gero (a common STOP/Djvu variant name), a file named document.docx would be renamed to [email protected]. The [original_4_char_extension] part can vary significantly between specific sub-variants (e.g., .mprg, .adlg, etc.).
  • Renaming Convention: The ransomware preserves the original filename and its extension, then appends its own unique extensions (the variant-specific one followed by [email protected]). For example:
    • photo.jpg becomes photo.jpg.[variant_name][email protected]
    • spreadsheet.xlsx becomes spreadsheet.xlsx.[variant_name][email protected]
      It also typically drops a ransom note named _readme.txt in every folder containing encrypted files.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family has been active since late 2018/early 2019 and continues to be one of the most prevalent ransomware threats. Specific variants like the one associated with [email protected] emerge periodically as part of the continuous evolution and deployment cycle of this ransomware family. While an exact start date for this specific email variant is difficult to pinpoint without specific threat intelligence reports, it would fall within the active period of the broader STOP/Djvu operations. New variants are often deployed weekly or even daily.

3. Primary Attack Vectors

  • Propagation Mechanisms: STOP/Djvu ransomware primarily targets individual users and small to medium-sized businesses through deceptive distribution methods. Its main propagation mechanisms include:
    • Bundled Software/Cracked Software: This is the most common vector. Users download “free” versions of paid software, keygens, software activators, or game cracks from unofficial websites, torrent sites, or peer-to-peer networks. The ransomware executable is hidden within these seemingly legitimate installers.
    • Fake Software Updates: Malicious websites or pop-up ads may prompt users to download fake updates for popular software (e.g., Flash Player, Java, web browsers), which are actually ransomware installers.
    • Malicious Advertisements (Malvertising): Compromised ad networks or malicious ads displayed on legitimate websites can redirect users to exploit kits or directly download the ransomware.
    • Compromised Websites: Visiting a compromised website can lead to drive-by downloads, though this is less common for Djvu than social engineering tricks.
    • Phishing Campaigns (Less Common for Djvu): While less prevalent for STOP/Djvu compared to other ransomware families, email attachments or malicious links delivered via phishing emails can also serve as an infection vector.
    • Remote Desktop Protocol (RDP) Exploits/Software Vulnerabilities (Rare for Djvu): Unlike enterprise-focused ransomware, STOP/Djvu typically does not exploit network vulnerabilities like EternalBlue or directly brute-force RDP. Its focus is more on individual user compromise through social engineering and deceptive downloads.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Regular, Offline Backups: Implement a robust backup strategy. Store critical data on external drives or cloud services that are not continuously connected to your network. This is the most effective defense against data loss.
    • Software and OS Updates: Keep your operating system (Windows, macOS, etc.) and all software applications (web browsers, office suites, antivirus) fully updated. Patches often fix vulnerabilities that attackers could exploit.
    • Reputable Antivirus/Endpoint Detection and Response (EDR): Use a high-quality antivirus solution with real-time protection and keep its definitions updated. For organizations, EDR solutions offer more advanced threat detection and response capabilities.
    • Software Download Caution: Avoid downloading software from unofficial sources, torrent sites, or unverified freeware/shareware websites. Always prefer official developer websites or trusted app stores.
    • Email and Web Browsing Hygiene: Be extremely cautious about opening suspicious email attachments or clicking on links from unknown senders. Use a browser with built-in security features and consider an ad-blocker to mitigate malvertising risks.
    • Network Segmentation: For businesses, segmenting your network can limit the lateral movement of ransomware if one system gets infected.
    • Principle of Least Privilege: Ensure users only have the necessary permissions to perform their tasks, limiting potential damage.

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 the ransomware from spreading to other devices.
    2. Identify and Terminate Processes: Boot the computer into Safe Mode with Networking. Open Task Manager and look for suspicious processes. It might be difficult to identify the exact ransomware process, but look for high CPU/disk usage processes that are unfamiliar.
    3. Scan with Antivirus/Anti-Malware: Run a full system scan using a reputable anti-malware tool (e.g., Malwarebytes, HitmanPro, your updated antivirus solution). Ensure the tool is updated to the latest definitions.
    4. Remove Ransomware Files: Allow the anti-malware software to quarantine or delete detected threats. Manually check common ransomware persistence locations:
      • %APPDATA%
      • %LOCALAPPDATA%
      • %PROGRAMDATA%
      • %TEMP%
      • C:\Users\<username>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup
      • Check Scheduled Tasks (Task Scheduler) and Startup programs for suspicious entries.
    5. Remove Ransom Notes: Delete all instances of _readme.txt files from your system once the ransomware executable is removed.
    6. Check Hosts File: STOP/Djvu often modifies the C:\Windows\System32\drivers\etc\hosts file to block access to security-related websites. Check this file and remove any suspicious entries that redirect security domains (e.g., google.com, antivirus sites) to 127.0.0.1.
    7. Scan External Drives: Any external hard drives or USB sticks connected during the infection should also be scanned.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Limited Decryption Possibility: Decrypting files encrypted by STOP/Djvu (including [email protected] variants) is only possible in specific circumstances.
      • Offline Keys: If the ransomware failed to establish a connection with its command-and-control (C2) server during encryption, it uses a limited set of “offline” encryption keys. For these cases, security researchers (like those at Emsisoft) can sometimes derive a universal decryptor.
      • Online Keys: If the ransomware successfully connected to its C2 server, it generates a unique “online” encryption key for each victim. Decrypting files encrypted with an online key is generally not possible without the specific private key held by the attackers.
    • Never Pay the Ransom: Paying the ransom does not guarantee decryption, encourages future attacks, and funds criminal activities.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP Djvu Ransomware: This is the primary tool for attempted decryption. It can test if your files were encrypted with an offline key that has been recovered. Download it ONLY from official sources (e.g., Emsisoft’s website). The decryptor requires a sample of an encrypted file and its original, unencrypted version (if available) to aid in key identification.
    • Data Recovery Software: Tools like Shadow Explorer (to recover Shadow Volume Copies, though Djvu often deletes them) or file recovery software (e.g., Recuva) might occasionally recover fragmented or deleted files, but this is often not effective for fully encrypted data.
    • Backups: The most reliable recovery method is restoring your data from clean, offline backups.

4. Other Critical Information

  • Additional Precautions:
    • Shadow Volume Copy Deletion: STOP/Djvu variants are known to delete Shadow Volume Copies using vssadmin.exe delete shadows /all /quiet, making built-in Windows recovery options (like Previous Versions) ineffective.
    • Hosts File Modification: As mentioned, it often modifies the hosts file to block access to security websites, hindering victims’ ability to seek help or download anti-malware tools.
    • Offline vs. Online Keys: Always remember the critical distinction between online and offline encryption keys. This determines the feasibility of public decryption tools.
    • Continuous Evolution: The STOP/Djvu family is constantly evolving, with new variants appearing regularly. This means decryption tools may take time to be updated, or may never be effective for some new online key variants.
  • Broader Impact:
    • Widespread Individual Impact: Due to its common distribution via pirated software, STOP/Djvu primarily impacts individual users and small businesses who may lack sophisticated security measures and regular backup routines.
    • Significant Data Loss: For victims without proper backups, this ransomware can lead to permanent loss of personal documents, photos, and critical business data.
    • Financial Burden: Beyond the potential ransom payment (which should be avoided), victims face costs associated with system cleanup, data recovery attempts, and potential professional IT support.
    • Reputational Damage: For businesses, a ransomware infection can lead to a loss of customer trust and operational downtime.

Combating the *[email protected]* ransomware variant, like other STOP/Djvu variants, hinges on proactive prevention and robust backup strategies. While decryption may be possible in some cases, it should not be relied upon as the primary recovery method.