Mydoom

Overview

Mydoom (cataloged historically under designations including Worm:Win32/Mydoom, W32.Mydoom@mm, W32.Novarg.A@mm, and Shimgapi) is one of the most prolific and fastest-spreading mass-mailing computer worms in internet history. First detected on January 26, 2004, Mydoom infected millions of computers worldwide, accounting for an estimated 25% of all global email traffic during its peak outbreak and prompting official emergency technical alerts from US-CERT (TA04-028A) and CISA. Distributed via deceptive email messages with spoofed senders and generic subject lines (e.g., 'Error', 'Status', 'Mail Delivery System'), Mydoom lured users into opening malicious attachments (.exe, .scr, .pif, .bat, or .zip). Once executed, Mydoom harvested email addresses from victim address books and local files (excluding security and educational domains) to broadcast mass copies via its own built-in SMTP engine. In addition to mass mailing, Mydoom opened an unauthorized listening backdoor on TCP ports 3127 through 3198 (specifically port 3127) and launched synchronized distributed denial-of-service (DDoS) SYN floods against the websites of the SCO Group and Microsoft.

Known aliases

Threat reports may refer to this family under multiple names:

• Worm:Win32/Mydoom
• W32.Mydoom@mm
• W32.Novarg.A@mm
• WORM_MIMAIL.R

Family Pedigree & Lineage

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

Derived From / Upstream Ancestry: Mimail Worm Family

Known Derivatives & Downstream Variants: Mydoom.A · Mydoom.B · Mydoom.M

MITRE ATT&CK Techniques

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

Tactical Mitigations

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

• T1036.004: Monitor for executable files running from unusual paths or with deceptive names. Use EDR to detect process masquerading.
• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

MITRE D3FEND™ Defensive Countermeasures

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

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.

• a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a7b8
• 1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e

Delivery vectors

• message.scr
• document.pif
• body.zip

Persistence mechanisms

• HKLM\Software\Microsoft\Windows\CurrentVersion\Run\TaskMon
• C:\Windows\System32\shimgapi.dll

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_MYDOOM_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Mydoom"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "mydoom" ascii wide nocase
        $s2 = "worm:win32/mydoom" ascii wide nocase
        $s3 = "w32.mydoom@mm" ascii wide nocase
        $s4 = "w32.novarg.a@mm" ascii wide nocase
        $s5 = "worm_mimail.r" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Mydoom (Worm) Execution & Triage
id: 61cd7039-626a-514b-8903-7fc89de6f1b6
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Mydoom 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/mydoom
- 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.worm
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1566_001
- attack.t1204_002
- attack.t1059_003
- attack.t1547_001
- attack.t1114_001
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_MYDOOM_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Mydoom 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 = "mydoom" 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. Quarantine the endpoint immediately to halt the outbound mass-mailing campaign and sever the active backdoor listening on TCP 3127.
2. Enforce egress firewall rules blocking outbound TCP port 25 from all endpoints, forcing all email traffic through authorized corporate mail relays.
3. Utilize EDR or network scanners to identify any hosts with open, listening ports in the 3127-3198 range.
4. Assume total endpoint compromise; perform a clean OS rebuild, as the backdoor was frequently used to install additional rootkits and malware.

What to Avoid

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

1. Do not ignore the infection as a 'low severity' spam issue; the open backdoor provides full remote command execution to any attacker.
2. Avoid assuming the threat is contained just by stopping the spam; ensure the initial vector is purged from all mailboxes.

References & External Analysis

• US-CERT / CISA Technical Alert TA04-028A - W32/Mydoom.A
• Huntress Threat Research - History of Mydoom
• CISA Advisory: TA04-028A
• Search "mydoom" on VirusTotal (External Analysis)
• Search "mydoom" on Any.Run (Sandbox Sandbox)
• Search "mydoom" 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: TA04-028A ↗

Frequently Asked Questions

Related Threats (Category: Worm)

Explore other documented threats in the same operational category:

• Beebone
• Ngrbot
• Warezov
• Sytro
• Brontok
• Perinet
• Kolabc
• Ludbaruma

Machine-readable

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