# Worm

A type of self-replicating malware that spreads across networks without needing a host file or human action.

**Worm[↗](/worm)** is a type of self-replicating malware[↗](/malware) that spreads automatically across networks and devices without needing to attach itself to a file or require any action from a user, unlike a virus, which typically needs a host program to run.

Because worms spread on their own, they can propagate extremely fast, sometimes infecting thousands of machines within hours by exploiting a single unpatched vulnerability[↗](/vulnerability). Famous examples have caused major internet-wide disruptions, which is why prompt patching remains one of the best defenses.