CyberGlossary

Malware

Computer Worm

Also known as: Network worm, Internet worm

Definition

Self-replicating malware that propagates across networks autonomously, without requiring a host file or user interaction.

A computer worm is malware that spreads by exploiting network services, open shares, or unpatched vulnerabilities, copying itself from system to system without needing to attach to a host program. Worms can saturate links, degrade services, deliver secondary payloads like ransomware or backdoors, and reach internal systems that are not directly exposed to the internet. Famous outbreaks include Morris (1988), SQL Slammer (2003), Conficker (2008), and WannaCry (2017). Defences include rapid patching of network-facing services, disabling legacy protocols (SMBv1, weak RDP), network segmentation, egress filtering, and detection of unusual lateral traffic patterns.

Examples

  • WannaCry, a ransomware worm exploiting EternalBlue in SMBv1.
  • Stuxnet, a worm that targeted Iranian centrifuges via USB and network paths.

Related terms