*@blocked

[Content by Gemini 2.5]

This resource provides a detailed technical breakdown and practical recovery strategies for the ransomware variant commonly identified by the file extension .blocked, often referred to as *@blocked due to its effect on files and potential indicators in ransom notes. This variant is a part of the prolific STOP/Djvu ransomware family.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by this ransomware variant will typically have the .blocked extension appended to their original name. For example, document.docx would become document.docx.blocked. While the prompt mentions *@blocked, the actual file extension added is most commonly .blocked, indicating the file is “blocked” from access. The *@blocked phrasing likely refers to the state of the files (being blocked) or is a shorthand identifier for a specific campaign or email address found within the ransom note (e.g., [email protected]).
  • Renaming Convention: The ransomware encrypts a wide range of file types (documents, images, videos, archives, databases, etc.) and then appends the .blocked extension. The original filename is preserved before the added extension.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Variants adding the .blocked extension, as part of the larger STOP/Djvu (also known as Djvu/STOP or .Puma) ransomware family, have been active and continuously evolving since late 2018. New variants with slightly different extensions and characteristics emerge regularly, making it one of the most persistent and widespread ransomware threats, primarily targeting individual users and small businesses.

3. Primary Attack Vectors

  • Propagation Mechanisms: The *@blocked variant (like most STOP/Djvu ransomware) primarily relies on deceptive methods to spread:
    • Software Cracks/Pirated Software: This is the most prevalent vector. Users download “cracked” versions of popular software (e.g., Adobe Photoshop, Microsoft Office, video games, VPNs, Windows activators) from torrent sites, free software download sites, or untrustworthy forums. The ransomware is often bundled within these executables.
    • Phishing Campaigns: While less common for STOP/Djvu than for enterprise-targeting ransomware, malicious attachments (e.g., seemingly legitimate invoices, shipping notifications, or resumes) in phishing emails can still deliver the payload.
    • Fake Software Updates: Websites mimicking legitimate software update notifications (e.g., for Flash Player, Java, web browsers) can prompt users to download and execute the ransomware.
    • Malvertising: Malicious advertisements on legitimate or compromised websites can redirect users to pages hosting exploit kits or directly downloading the ransomware.
    • Compromised Remote Desktop Protocol (RDP): Less common for this family but still possible, attackers may brute-force weak RDP credentials to gain access and manually deploy the ransomware.
    • Drive-by Downloads: Visiting a compromised website can sometimes trigger an automatic download of the malicious payload without explicit user interaction, especially if the browser or OS has unpatched vulnerabilities.

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/cloud). Ensure backups are isolated from the network to prevent encryption.
    • Reputable Anti-Malware Software: Install and maintain up-to-date antivirus/anti-malware software with real-time protection.
    • Software Updates & Patching: Keep operating systems, applications (browsers, office suites, PDF readers, etc.), and antivirus definitions fully patched to close known security vulnerabilities.
    • User Education: Train users to recognize phishing attempts, suspicious attachments, and the dangers of downloading software from untrusted sources.
    • Strong Passwords & MFA: Use strong, unique passwords for all accounts, especially for RDP and administrative access. Enable Multi-Factor Authentication (MFA) wherever possible.
    • Disable Unnecessary Services: Disable SMBv1 and close unnecessary ports, especially RDP if not regularly used or not secured behind a VPN.
    • Firewall Rules: Configure firewalls to block unauthorized inbound and outbound connections.

2. Removal

  • Infection Cleanup:
    1. Isolate the Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet cable, disable Wi-Fi). This prevents further spread to other devices.
    2. Identify and Terminate Ransomware Processes: Boot the computer into Safe Mode with Networking (if possible). Use Task Manager (Ctrl+Shift+Esc) to identify and end suspicious processes. Ransomware often runs under generic names or disguised as legitimate system processes.
    3. Scan with Reputable Anti-Malware: Perform a full system scan using your updated anti-malware software (e.g., Malwarebytes, Kaspersky, Bitdefender, Windows Defender). This will identify and remove the ransomware executable and any associated malicious files. It’s often recommended to run scans from multiple vendors if possible.
    4. Remove Persistence Mechanisms: Check common ransomware persistence locations:
      • Registry: Use regedit to look for suspicious entries in HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run, HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run, and similar keys.
      • Startup Folders: Check shell:startup and shell:common startup.
      • Task Scheduler: Look for newly created, suspicious scheduled tasks.
    5. Remove Shadow Volume Copies: Ransomware often deletes Shadow Volume Copies to prevent easy restoration. However, it’s good practice to attempt to restore them if the ransomware failed to delete them fully, or if they were created after the deletion attempt. Use vssadmin delete shadows /all /quiet (though this also removes legitimate ones) or a tool like ShadowExplorer to manage.

3. File Decryption & Recovery

  • Recovery Feasibility: Decrypting files encrypted by STOP/Djvu .blocked variants without the attacker’s private key is challenging but sometimes possible:
    • Online vs. Offline Keys: STOP/Djvu ransomware uses a unique encryption key for each victim. If the victim’s system is offline or fails to connect to the attacker’s server during encryption, it uses an “offline key,” which is one of a limited set of default keys. If an offline key is used, decryption is often possible if security researchers have obtained or reverse-engineered that specific offline key. If the system is online, a unique “online key” is generated and used, making decryption without the specific key virtually impossible.
    • Methods/Tools Available:
      • Emsisoft Decryptor for STOP/Djvu: This is the primary tool for attempting decryption. Developed by Emsisoft in collaboration with Michael Gillespie (MalwareHunterTeam), it is regularly updated with new offline keys as they are discovered.
        • How it works: You provide the decrypter with a pair of encrypted and original (unencrypted) files. If an offline key matches, or if a known offline key is found for your variant, it can decrypt files.
        • Note: If the decryptor says “No key for ID,” it means your specific online key is not available, and decryption is currently not possible.
      • File Recovery Software: For highly corrupted or partially encrypted files, or if shadow copies were not deleted, tools like PhotoRec, Recuva, or Disk Drill might recover older, unencrypted versions of files. This is often a long shot for fully encrypted files.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP/Djvu: (Download from Emsisoft’s official website)
    • Reputable Anti-Malware Software: (e.g., Malwarebytes, Bitdefender, Kaspersky, ESET, Windows Defender)
    • Backup Solutions: (e.g., external hard drives, cloud storage like Google Drive, OneDrive, Dropbox, or dedicated backup software)
    • Windows Security Updates: Ensure your Windows OS is fully updated via Windows Update.

4. Other Critical Information

  • Additional Precautions:
    • Info-Stealer Malware: *@blocked and other STOP/Djvu variants are notorious for often being bundled with information-stealing malware (e.g., Vidar, Azorult, RedLine Stealer, SmokeLoader). This means that beyond file encryption, your sensitive data (passwords, cryptocurrency wallets, browser data, system info) might have been exfiltrated. It is highly recommended to change all critical passwords (email, banking, social media, etc.) from a clean, uninfected device after the infection is completely removed.
    • Ransom Note: The ransomware typically drops a ransom note named _readme.txt (or similar) in every folder containing encrypted files, and often on the desktop. This note provides instructions on how to contact the attackers and pay the ransom (usually in Bitcoin) to receive the decryption key.
    • No Guarantees with Payment: Paying the ransom is strongly discouraged. There is no guarantee you will receive the decryption key, and it fuels the ransomware ecosystem, encouraging further attacks. Many victims who pay do not get their files back or only receive a partial decryption.
  • Broader Impact: The STOP/Djvu family, including the *@blocked variant, has a significant broader impact due to its high volume and continuous evolution. It disproportionately affects individual users and small to medium-sized businesses (SMBs) who may lack robust cybersecurity defenses and backup strategies, leading to significant data loss and financial strain. Its reliance on user-initiated execution (via pirated software) highlights the critical need for user education and responsible online behavior.