Worm

A worm locates a computer’s vulnerability and spreads within its connected network like an infection, while continually seeking new vulnerabilities. Like viruses, worms often originate from e-mail attachments that appear to be from trusted senders. Worms then spread to a user’s contacts via his e-mail account and address book.

Some worms spread and then do nothing while tthers cause harm. In such cases, the worm’s code is known as payload.