Worm

A worm is a type of malware that spreads automatically from one computer to another across a network, without needing a user to open a file or click a link.

Unlike a virus, which typically attaches to a file and relies on someone to run it, a worm copies itself by exploiting vulnerabilities, weak passwords or open network services. Once inside one machine, it scans for other vulnerable systems and infects them, sometimes within minutes. Some well-known ransomware outbreaks have used worm-like behaviour to spread rapidly across entire organizations.

For a small business with a flat network, a worm that reaches one unpatched computer can quickly spread to servers and other workstations, causing widespread disruption. Because no human action is required after the first infection, damage can occur faster than staff can react.

Practical tip: the main defences are prompt patching, network segmentation that limits how far malware can travel, and turning off network services that are not needed. Endpoint detection and response tools can spot and isolate infected devices automatically, which is especially valuable outside business hours.