MyDoom virus: What it is and why it mattered In January 2004 a mass-mailing worm called MyDoom began spreading through email inboxes worldwide, reaching hundreds of countries within days. MyDoom was a worm (not a file‑destroying virus) that replicated by tricking users into opening infected email attachments. Once executed, it harvested email addresses from the system and automatically sent copies of itself to new recipients. Two main variants circulated: MyDoom.A launched a large-scale distributed denial-of-service (DDoS) attack against the SCO Group, and MyDoom.B targeted Microsoft. The worm also installed a backdoor by opening specific TCP ports (roughly 3127–3198), enabling remote control of infected machines and forming botnets for coordinated attacks. Some versions attempted to spread via peer-to-peer file‑sharing networks, but email was the primary vector. MyDoom’s success came from simplicity and user behavior: emails mimicked delivery errors or system notifications with generic subject lines like “Error,” “Mail Delivery System,” or “Test,” so recipients were likely to open attachments. At the time, email filtering and antivirus tools were less effective and internet infrastructure had less capacity, allowing the outbreak to generate massive volumes of traffic and strain servers and ISPs. Impact: MyDoom caused sluggish systems, congested inboxes, lost productivity, and widespread network slowdowns. At its peak it accounted for a large share of global email traffic; contemporary estimates put its economic impact in the tens of billions of dollars. MyDoom is no longer an active widespread threat, though traces may appear on legacy systems, in research samples, or when reused code triggers detections. Legacy: The outbreak influenced modern security practices: improved email filtering, behavior-based detection, faster threat intelligence sharing, and multi-layered defenses. Key lessons include skepticism toward unexpected attachments, verifying sender addresses, pausing before acting on urgent messages, keeping systems updated, and combining user awareness with modern anti-malware tools.
