Virlock

Overview

VirLock (tracked in academic literature and threat databases as VirRansom) represents a historic and technically unique evolutionary milestone in malware engineering: it was the world's first documented hybrid between a parasitic polymorphic file infector and a screen-locking ransomware locker. First surfacing in December 2014, VirLock diverged drastically from standard ransomware families that simply encrypt target files and append static extensions. Instead of in-place encryption, VirLock acts as a classic virus: it infects existing files on the host—including Windows executables (.exe), Word documents (.doc), Excel spreadsheets (.xls), PDF files (.pdf), and archive volumes (.zip)—by encrypting the original host body, generating a polymorphic decryption stub, and prepending or appending the malware's own executable code directly into the target file. Consequently, every single infected file on the victim's hard drive or mapped network share is transformed into a functioning VirLock executable. When any infected file is subsequently executed, VirLock executes its payload, establishes persistence via registry Run keys, terminates security software processes, and presents a full-screen lockscreen pretending to originate from federal law enforcement (claiming copyright infringement or software piracy) demanding a Bitcoin fine to unlock the machine. Because every infected document becomes an active vector, VirLock spreads rapidly across shared enterprise file servers and removable USB media, requiring specialized cryptographic disinfection rather than simple quarantine.

Known aliases

Threat reports may refer to this family under multiple names:

• VirLock
• VirRansom
• Polymorphic Locker

Threat Actor Attribution

Attribution is probabilistic, not a science. Each link below states its confidence level and the evidence behind it.

• Underground Eastern European Virus Writers High confidence
  Basis: Authored by experienced polymorphic virus developers incorporating advanced Win32 assembly infector mechanics with modern Bitcoin extortion schemes. [source]

Family Pedigree & Lineage

Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:

Known Derivatives & Downstream Variants: Virlock V1 · Virlock V2 (Cloud Spreader) · Virlock Shape-Shifter

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

Command & Control (C2) and Network Profile

How this family talks to its operators. C2 traffic can often identify a family even when its code and configuration are hard to analyse. Ports and patterns are historical and change between campaigns, so use them as hunting leads rather than block-only rules.

Network detection ideas

• Detect rapid modification and rewriting of executable and office document headers across network shares
• Monitor for unexpected executable file extensions (.exe) appended to document names
• Flag high-frequency file write operations characteristic of mass polymorphic infection

Sources: CISA StopRansomware Resource Hub, Virus Bulletin: The VirLock Polymorphic Hybrid Analysis

Indicators of Compromise

Public indicators drawn from CISA advisories and vendor reporting. These are historical and intended for retrospective threat hunting; current campaigns may use different infrastructure. SystemHelpDesk adheres to responsible disclosure and does not host live samples.

File hashes (SHA-256, sample)

Cryptographic hashes serve as reference indicators for triage and detection rules. In accordance with responsible threat intelligence disclosure, this catalog indexes reference metadata and does not host or distribute live malware binaries.

• d9021e1f13b190f842323e05a8d9a244b413155106518db62c94bb2e20516801
• b44ef911bc1bb910bc4928120ecba094b8e612ec9103cba214a12ec98b0f948e

Delivery vectors

• Peer-to-peer (P2P) file sharing networks distributing infected software installers
• Removable USB storage drives carrying files infected by VirLock's parasitic routine

Persistence mechanisms

• Registry Run key in HKCU\Software\Microsoft\Windows\CurrentVersion\Run pointing to an infected .exe
• Hijacking user shell settings in Winlogon registry keys to enforce screen lock upon reboot

Tiered Detection Rules (Cisco CAIRN Model)

Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:

rule MALWARE_WIN_VIRLOCK_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Virlock"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "virlock" ascii wide nocase
        $s2 = "virlock" ascii wide nocase
        $s3 = "virransom" ascii wide nocase
        $s4 = "polymorphic locker" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Virlock (Ransomware File Infector) Execution & Triage
id: 1a5c9855-5610-51fc-af7e-587bbc5150ad
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Virlock malware family. Detects suspicious execution from temporary user
  directories with hidden window flags and background transfer utilities.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/virlock
- https://malware-families-catalog.systemhelpdesk.com/defensive/ransomware-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.ransomware-file-infector
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1486
- attack.t1027_009
- attack.t1055
- attack.t1547_001
- attack.t1070_004
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \cmd.exe
    - \powershell.exe
    - \cscript.exe
    - \wscript.exe
    CommandLine|contains:
    - AppData\Local\Temp
    - -WindowStyle Hidden
    - /e:jscript
    - bitsadmin /transfer
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: medium

rule MALWARE_WIN_VIRLOCK_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Virlock tradecraft"
        tier = "T3 - Attribution Fingerprint"
        confidence = "High (Confirmed Family Signature)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        // Core family identifier & heuristic payload signatures
        $attrib_str = "virlock" ascii wide nocase
        $pe_magic = "MZ" ascii
        $net_marker = "http" ascii nocase
    condition:
        uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}

Containment & Response Steps

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

1. Immediately disconnect the system from all local and network shared storage to prevent virus propagation.
2. Do not delete infected files; VirLock embeds the original document inside the infected executable container.
3. Use dedicated vendor disinfection tools (e.g. specialized decrypters) capable of stripping the polymorphic stub and restoring the original file body.
4. Restore network shares from immutable, air-gapped backups captured prior to the outbreak.
5. Scan all attached USB and secondary storage media before reconnecting to the environment.

What to Avoid

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

1. Do not run automated 'quarantine and delete' antivirus rules, as this will destroy the original files embedded inside the infected wrappers.
2. Do not pay the ransom note, as VirLock's file restoration capabilities are notoriously unreliable when executed by the attacker's decryptor.

References & External Analysis

• Virus Bulletin: "VB2015 paper: It’s A File Infector... It’s Ransomware... It’s Virlock" (Nacu, Androinic, Craciun)
• CISA Advisory: CISA Alert AA21-209A (Ransomware Evolution & Polymorphic Threats)
• Search "virlock" on VirusTotal (External Analysis)
• Search "virlock" on Any.Run (Sandbox Sandbox)
• Search "virlock" on MalwareBazaar (Malware Samples)

North American Authority Advisory (CISA / NIST)

The Cybersecurity and Infrastructure Security Agency (CISA) has published an official US federal advisory on this family, which can be mapped to NIST Cybersecurity Framework (CSF) incident response controls: CISA Alert AA21-209A (Ransomware Evolution & Polymorphic Threats) ↗

Frequently Asked Questions

Related Threats (Category: Ransomware)

Explore other documented threats in the same operational category:

• Bnuaaewgb2Fb
• Protector
• Sahat
• Rmkef9Zs0Zhi
• Meinhudong
• Machaer
• Atomix
• Trialkiller

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/virlock.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.