*[email protected]*

[Content by Gemini 2.5]

The string *[email protected]* points to a variant of the prolific STOP/Djvu ransomware family. While the string itself is most commonly the contact email address found in the ransom note, it’s also sometimes indicative of the specific variant or, less commonly, directly incorporated into the encrypted file extension. For clarity, this resource will describe the characteristics of a STOP/Djvu variant associated with the [email protected] contact email.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    STOP/Djvu ransomware variants, including the one identified by [email protected], encrypt files and append a unique, often 3-4 character, extension to them. Common examples for this family include .cho, .dambler (the email itself is often part of the variant name or contact), .adame, .bopd, .kodi, etc. The specific extension for the variant associated with [email protected] could be .cho, .dambler, or another variant-specific string. It is highly unlikely the entire email address [email protected] would be the literal file extension.
  • Renaming Convention:
    The ransomware renames encrypted files by appending its unique extension after the original file extension.
    • Example: A file named document.docx would become document.docx.[variant_extension] (e.g., document.docx.cho or document.docx.dambler).
    • A ransom note file, typically named _readme.txt, is dropped in every folder containing encrypted files. This note contains instructions for the victim, including the demand for cryptocurrency (usually Bitcoin) and the contact email address, which in this case would be [email protected] (or similar, like [email protected], [email protected], etc., for other variants).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    The STOP/Djvu ransomware family has been active since late 2017/early 2018 and is one of the most consistently active and evolving ransomware threats. New variants, often identified by their unique file extensions and contact emails, emerge constantly, sometimes on a daily basis. The [email protected] identifier suggests a specific wave or minor variant within this ongoing campaign.

3. Primary Attack Vectors

STOP/Djvu ransomware primarily relies on social engineering tactics and deceptive delivery methods rather than sophisticated network exploits.

  • Propagation Mechanisms:
    • Software Cracks and Pirated Software: This is the most prevalent infection vector. Users download seemingly legitimate cracked software, key generators, activators, or game cheats from unofficial websites, torrents, or file-sharing platforms. The ransomware is often bundled silently within these seemingly harmless executables.
    • Malicious Email Attachments: Less common for Djvu than for other families, but still a possibility. Phishing emails may contain infected attachments (e.g., seemingly legitimate documents with malicious macros, or executable files disguised as invoices or shipping notifications).
    • Fake Software Updates: Pop-ups or deceptive websites claiming to offer critical software updates (e.g., Flash Player, Java, web browsers) can deliver the ransomware payload.
    • Malvertising and Exploit Kits (Less Common Now): While historically a vector for various malware, Djvu’s primary distribution has shifted away from large-scale exploit kit campaigns towards direct user downloads. However, malicious advertisements can still lead to infected downloads.
    • Bundled with Legitimate Software: Less reputable download sites might bundle the ransomware with free software during installation.
    • Remote Desktop Protocol (RDP) Exploits / Brute-forcing: While not the primary method for initial infection with Djvu, compromised RDP credentials or weak RDP security could allow an attacker to manually deploy the ransomware onto a system. This is more common with enterprise-targeting ransomware.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Regular Backups: Implement a robust 3-2-1 backup strategy (3 copies of data, on 2 different media, with 1 offsite/offline). Ensure backups are isolated from the network to prevent encryption.
    • Robust Endpoint Security: Install and maintain up-to-date antivirus and anti-malware software with real-time protection and behavioral detection capabilities on all devices.
    • Software Updates & Patching: Keep operating systems, applications, and all software (especially web browsers, office suites, and security software) fully patched. Enable automatic updates where feasible.
    • User Education: Train users about the risks of downloading pirated software, opening suspicious email attachments, clicking on dubious links, and the dangers of unofficial download sites.
    • Strong Password Policies & Multi-Factor Authentication (MFA): Implement strong, unique passwords and MFA for all critical accounts, especially those with administrative privileges or RDP access.
    • Disable Auto-run: Configure operating systems to disable auto-run features for external media.
    • Principle of Least Privilege: Limit user permissions to only what is necessary for their job functions. Avoid browsing or performing daily tasks with administrative accounts.

2. Removal

  • Infection Cleanup:
    1. Isolate the Infected System: Immediately disconnect the infected computer from the network (both wired and Wi-Fi) to prevent further spread to other devices.
    2. Identify the Ransomware Process: Use Task Manager (Ctrl+Shift+Esc) to look for unusual processes consuming high CPU or disk resources. The ransomware executable often has a random or disguised name.
    3. Boot into Safe Mode: Restart the computer in Safe Mode with Networking. This loads only essential drivers and services, preventing the ransomware from fully executing.
    4. Run Full System Scans: Use reputable anti-malware tools (e.g., Malwarebytes, ESET, Sophos, Microsoft Defender) to perform a full system scan. Ensure definitions are updated before scanning.
    5. Remove Detected Threats: Allow the anti-malware software to quarantine or remove all identified threats.
    6. Check Startup Items and Scheduled Tasks: Manually review and remove any suspicious entries in msconfig (Startup tab) or Task Scheduler (taskschd.msc) that might re-launch the ransomware.
    7. Delete Ransomware Files: Search for and delete any remaining ransomware executables or associated files. These often reside in %AppData%, %Temp%, or %ProgramData% folders, often with random filenames.
    8. Restore Host File: Djvu variants often modify the hosts file (C:\Windows\System32\drivers\etc\hosts) to block access to security-related websites. Restore it to its default state or remove malicious entries.
    9. Change All Passwords: After the system is clean, change all passwords, especially for accounts accessed from the infected machine.

3. File Decryption & Recovery

  • Recovery Feasibility:
    The possibility of decrypting files encrypted by STOP/Djvu ransomware depends heavily on whether an online key or an offline key was used during the encryption process.
    • Online Key: If the ransomware successfully contacted its Command & Control (C2) server, it generates a unique encryption key for the victim, which is then stored on the C2 server. In this scenario, decryption is extremely difficult, if not impossible, without the attacker’s master key. This is the most common scenario for Djvu infections.
    • Offline Key: If the ransomware fails to connect to its C2 server (e.g., due to network issues or server shutdown), it often resorts to using a pre-generated “offline” key from a limited pool. If security researchers have managed to obtain or deduce the specific offline key used by your variant, then decryption might be possible.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP Djvu: This is the primary and most reputable tool for attempting decryption. It works by analyzing encrypted files and comparing them to known patterns or a few original (unencrypted) files you might still have (e.g., from email attachments or other sources). If an offline key matches, or if Emsisoft’s researchers have found the online key (rare), it might be able to decrypt your files. It’s crucial to understand that success is not guaranteed, especially with online keys.
    • Shadow Volume Copies: Ransomware typically attempts to delete Shadow Volume Copies (VSS) using commands like vssadmin.exe Delete Shadows /All /Quiet. However, sometimes this deletion fails or is incomplete. You can try using tools like ShadowExplorer to see if any previous versions of files are recoverable.
    • System Restore Points: Similar to VSS, ransomware often targets system restore points. Check if any are available.
    • Professional Data Recovery Services: For highly critical data without backups, specialized data recovery firms might offer assistance. However, this is very expensive and still no guarantee of success for encrypted files.
    • The most effective “tool” for recovery remains up-to-date, isolated backups.

4. Other Critical Information

  • Additional Precautions:
    • Host File Modification: STOP/Djvu often modifies the Windows hosts file to redirect or block access to cybersecurity websites, making it harder for victims to seek help or download security tools. Always check and restore your hosts file after an infection.
    • Persistence Mechanisms: The ransomware often creates scheduled tasks or registry entries to ensure it re-executes on system startup, even if the main executable is deleted. Thorough cleanup is essential.
    • Information Stealer Modules: Many Djvu variants are bundled with other malware, most notably information stealers like Vidar or RedLine Stealer. These additional payloads attempt to exfiltrate sensitive data such as browser passwords, cryptocurrency wallet information, and banking credentials. Even if files are recovered, assume personal data might have been compromised.
  • Broader Impact:
    • High Volume Consumer Threat: STOP/Djvu is one of the most widespread ransomware families targeting individual users and small businesses. Its simple distribution method via pirated software makes it highly effective at infecting a large number of victims.
    • Significant Data Loss: Due to the prevalence of online keys, many victims face permanent data loss if they do not have robust backups.
    • Financial Strain: The ransom demands are typically lower than those for enterprise-level ransomware, but still significant enough to cause financial strain for individuals and small entities.
    • Emotional Distress: The loss of irreplaceable personal files (photos, videos, documents) can cause immense emotional distress for victims.
    • Ongoing Threat: The continuous development of new variants ensures Djvu remains a persistent and evolving threat that requires constant vigilance.