Stop

Overview

Ransomware:Win32/Stop (widely known as STOP/Djvu) is arguably the most widely distributed ransomware family in the world by raw infection volume. Unlike enterprise-focused cartels (like LockBit or ALPHV), STOP/Djvu almost exclusively targets home users and consumers. It achieves massive scale by embedding itself entirely within the ecosystem of software piracy: cracked software, keygens, and torrents (`T1566.002`).

Understanding STOP / Djvu (Consumer Ransomware)
To a home user, the infection is devastating: personal photos, documents, and game saves are encrypted, appended with a 4-letter extension (e.g., `.djvu`, `.rumba`, `.qewe`), and a `_readme.txt` file demands a ransom (usually $490-$980 in Bitcoin). For security researchers, STOP is notable for its sheer volume and its secondary payload: it almost always drops the RedLine or Vidar infostealer (`T1056`) *before* encrypting, ensuring the attackers profit from stolen credentials even if the victim refuses to pay the ransom.

Execution and Cryptographic Mechanics
STOP/Djvu is distributed via drive-by downloads on illegal software cracking sites. When the user executes the 'crack', the ransomware runs. It disables Windows Defender, kills running processes (to free up files for encryption), and contacts its C2 server to retrieve a unique 'Online' RSA public key (`T1486`). If the C2 server is unreachable, it defaults to a hardcoded 'Offline' key (which security researchers have often managed to crack). It then uses Salsa20 to encrypt files. Crucially, it modifies the Windows `HOSTS` file (`T1562.002`) to block access to security vendor websites, preventing the victim from downloading help or decryptors.

Indicators of Compromise & Impact
The impact is total personal data loss and the theft of all browser passwords and session cookies (via the bundled infostealer). Host-based IoCs include files appended with the specific variant's 4-letter extension, the presence of the `_readme.txt` ransom note, and modifications to `C:\Windows\System32\drivers\etc\hosts` blocking sites like BleepingComputer or Microsoft. Network IoCs include the initial beacon to the C2 server to retrieve the encryption key.

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1056: Monitor for unauthorized keylogging, screen capturing, or web browser API hooking. Deploy EDR to detect API hooking.
• T1566.002: Inspect email links for known malicious domains and use link-rewriting services for time-of-click analysis.

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_STOP {
    meta:
        description = "Detects Stop (ransomware)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "stop" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Stop Activity
id: ef399b2d446bb37b7c32ad2cc1b6045b
status: experimental
description: Detects generic indicators of the stop malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*stop*"
    condition: selection
level: medium

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

1. Immediately disconnect the infected machine from the network. Do NOT reboot it, as live memory may hold the offline encryption keys.
2. Determine if the encryption used an 'Online' or 'Offline' key (Emsisoft provides a free tool for this); offline keys can often be decrypted for free.
3. Assume all passwords saved in the web browser (email, banking, social media) have been stolen by the bundled infostealer; reset them from a clean device.
4. Check the `HOSTS` file and remove entries blocking security websites so you can download necessary removal tools.

What to Avoid

Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.

1. Do not pay the ransom. STOP/Djvu operators have a terrible track record of actually providing working decryptors after payment.
2. Avoid focusing solely on the encryption; you must assume an infostealer ran first, meaning a full credential reset is mandatory.

References & External Analysis

• Search "stop" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: ransomware)

Explore other malware families in the same category:

• Zenfly
• Broskod
• Alphaeon
• Zudochka
• Forbot

Machine-readable

Get this profile as JSON: https://jordanricky1604-ship-it.github.io/malware-families-catalog/api/stop.json

Ecosystem & Interactive Environments

This profile is part of the Malware Families Catalog, a public dataset of 2,899 malware families. The catalog is also published across our ecosystem: Hugging Face, Kaggle, Zenodo, Replit, StackBlitz, CodeSandbox, and CodePen.