+readme-warning+.txt

[Content by Gemini 2.5]

The file +readme-warning+.txt is the signature ransom note filename used by the STOP/Djvu ransomware family, one of the most prolific and constantly evolving ransomware variants. While the ransom note remains consistent, the file extensions added to encrypted files change frequently. This detailed resource will focus on the STOP/Djvu ransomware, as +readme-warning+.txt is its primary identifier.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The string +readme-warning+.txt is not the file extension used to encrypt files. Instead, it is the filename of the ransom note dropped by the STOP/Djvu ransomware on affected systems. This note typically contains instructions for payment and contact information for the attackers.
  • Renaming Convention: STOP/Djvu ransomware encrypts files and appends a specific, often four-character, extension to the original filename. This extension varies with almost every new variant.
    • Typical Pattern: original_filename.extension.new_random_extension
    • Examples of past extensions: .djvu, .maas, .mado, .mkp, .kool, .oplh, .nasoh, .repp, .lokf, .npsg, .gero, .lqqm, and hundreds more.
    • For instance, a file named document.docx might become document.docx.mkp or document.docx.npsg.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family first emerged around late 2018 / early 2019 and has since become one of the most widely distributed ransomware variants, particularly targeting individual users and small businesses. It has maintained a high level of activity and evolution, with new variants appearing almost daily.

3. Primary Attack Vectors

STOP/Djvu primarily leverages social engineering and illicit software distribution channels:

  • Cracked Software & Pirated Content: This is by far the most prevalent infection vector. Users download seemingly legitimate cracked software, key generators (keygens), software activators, or pirated media (movies, music, games) from unofficial websites, torrents, or file-sharing services. These downloads are often bundled with the ransomware dropper.
  • Fake Software Updates/Installers: The ransomware can be disguised as installers or updates for popular software (e.g., Flash Player, video codecs, browser updates) found on malicious or compromised websites.
  • Malicious Websites/Drive-by Downloads: Visiting compromised websites or clicking on malicious advertisements can sometimes lead to a drive-by download of the ransomware dropper, though this is less common than direct download of cracked software.
  • Phishing Campaigns: While less prominent than software piracy for initial infection, phishing emails containing malicious attachments or links can also deliver STOP/Djvu, often disguised as invoices, shipping notifications, or other legitimate-looking communications.
  • Remote Desktop Protocol (RDP) Exploitation: While not the primary method for STOP/Djvu’s widespread distribution to individual users, compromised or weakly secured RDP credentials can be exploited by attackers to manually deploy the ransomware onto business networks.

Remediation & Recovery Strategies:

1. Prevention

Proactive measures are crucial to defend against STOP/Djvu ransomware:

  • Regular Backups (3-2-1 Rule): Implement a robust backup strategy (at least three copies of data, stored on two different media types, with one copy offsite or offline). Ensure backups are isolated from the network to prevent encryption.
  • Reputable Antivirus/Endpoint Detection and Response (EDR): Deploy and regularly update high-quality antivirus software or EDR solutions on all endpoints. Many security vendors have signatures and behavioral analysis to detect STOP/Djvu.
  • Software and OS Updates: Keep your operating system, applications, and security software fully patched and up-to-date. Attackers often exploit known vulnerabilities.
  • User Education: Train users about the dangers of downloading cracked software, pirated content, clicking suspicious links, and opening attachments from unknown senders. Emphasize the risks associated with unofficial download sites.
  • Firewall Configuration: Employ a robust firewall to block unauthorized inbound and outbound connections.
  • Disable Macros (if applicable): Configure Microsoft Office and other applications to disable macros by default or prompt users before enabling them, especially for files from external sources.
  • Ad-Blockers: Use reputable ad-blocking browser extensions to reduce exposure to malicious advertisements that could lead to drive-by downloads.
  • Principle of Least Privilege: Limit user permissions to only what is necessary for their role, reducing the impact if an account is compromised.

2. Removal

If a system is infected, follow these steps to remove the ransomware:

  • Isolate Immediately: Disconnect the infected computer from all networks (Wi-Fi, Ethernet, external drives) to prevent the ransomware from spreading to other devices.
  • Identify Ransomware Processes: Boot the system into Safe Mode with Networking (if possible) or Safe Mode without Networking to prevent the ransomware from executing fully or communicating with its command-and-control server.
  • Run Comprehensive Scans: Use reputable anti-malware and antivirus tools (e.g., Malwarebytes, Emsisoft Emergency Kit, HitmanPro, or your installed AV) to perform full system scans. These tools are often effective at detecting and removing the ransomware executable and associated components.
  • Check for Persistence: Manually check common persistence locations:
    • Registry Keys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run, HKLM\Software\Microsoft\Windows\CurrentVersion\Run
    • Startup Folders: %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup
    • Scheduled Tasks: Use Task Scheduler to look for suspicious tasks.
  • Remove Identified Threats: Follow the prompts from your security software to quarantine or delete all detected malicious files and registry entries.
  • Review System Changes: Check for new user accounts, disabled security features, or other unusual system modifications made by the ransomware. Restore these to their default settings.
  • Change Passwords: Once the system is confirmed clean, change all passwords used on the infected machine, especially for online accounts, if there’s any suspicion of data theft (which is common with Djvu).

3. File Decryption & Recovery

  • Recovery Feasibility: Decrypting files encrypted by STOP/Djvu ransomware is challenging and often depends on whether an “offline key” or “online key” was used during encryption.
    • Online Key: If the victim’s computer had an active internet connection when encrypted, the ransomware typically generates a unique encryption key for that victim, which is sent to the attacker’s server. This makes universal decryption almost impossible without the attacker’s private key.
    • Offline Key: If the victim’s computer was offline or couldn’t connect to the command-and-control server during encryption, the ransomware uses a pre-set “offline key.” These offline keys are shared across a group of victims, making it possible for security researchers to eventually discover and publish them, allowing for decryption.
  • Methods or Tools Available:
    • Emsisoft Decryptor for STOP/Djvu: This is the primary and most reliable tool for attempting decryption. Emsisoft, often in collaboration with academic researchers and law enforcement, continuously updates its decryptor as new offline keys are discovered.
      • How to Use: Download the decryptor from Emsisoft’s official website. Run it and point it to an encrypted file and its original (unencrypted) version if possible, or a folder containing encrypted files. The decryptor will attempt to identify the variant and apply known decryption keys.
      • Limitations: This decryptor will only work if an offline key was used and that key is known to Emsisoft. It typically cannot decrypt files encrypted with a unique online key.
    • Data Recovery Software (Limited Success): In some cases, if shadow copies were deleted but not fully overwritten, data recovery software might be able to retrieve older, unencrypted versions of files. However, this is rarely fully successful due to the way ransomware typically operates.
    • NEVER Pay the Ransom: Paying the ransom does not guarantee decryption and funds criminal activities. There is no assurance the attackers will provide a working key, and it marks you as a willing target for future attacks.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP/Djvu: The go-to tool for decryption attempts.
    • Reputable Antivirus/Anti-malware Suites: For removal and ongoing protection.
    • Operating System Patches: Keep Windows (or macOS/Linux if targeted) fully updated.
    • Browser Security Tools: Ad-blockers, script blockers, and browser security extensions can help prevent access to malicious sites.

4. Other Critical Information

  • Additional Precautions (Unique Characteristics):

    • Information Stealer Component: Many recent STOP/Djvu variants are bundled with information-stealing malware (e.g., Vidar, RedLine Stealer). This means that even if you can decrypt your files, your sensitive data (passwords, cryptocurrency wallets, browser history, financial information) may have already been exfiltrated. It’s crucial to assume data compromise and change all passwords for online services, especially financial and email accounts, after an infection.
    • Rapid Variant Evolution: The sheer number of new extensions and variants makes it challenging for decryptor tools to keep up. This means a decryptor might work for one variant but not for another, even if they share the same +readme-warning+.txt note.
    • Targeting: While ransomware like Conti or LockBit often targets large enterprises, STOP/Djvu historically targets individual users and small to medium-sized businesses, making it a pervasive threat for everyday computer users.
    • Self-Deletion and Persistence: After encryption, the ransomware often attempts to delete itself to hinder analysis and hide its presence, while setting up persistence mechanisms (e.g., scheduled tasks) to ensure a complete encryption process.

  • Broader Impact:

    • Widespread Financial Losses: Due to its high prevalence, STOP/Djvu has caused significant financial losses for countless individuals and small businesses, both from downtime and potential ransom payments (if victims choose to pay, which is discouraged).
    • Data Loss: When decryption is not possible and backups are absent or compromised, STOP/Djvu leads to permanent data loss, impacting personal memories, academic work, and business operations.
    • Erosion of Trust: The constant threat of ransomware like STOP/Djvu erodes user trust in online downloads and digital security, leading to increased anxiety and reduced productivity.
    • Fueling Cybercrime Ecosystem: The profitability of STOP/Djvu contributes to the larger cybercrime economy, funding further malicious activities and development of more sophisticated threats.