MyDoom is a computer worm that was first discovered in January 2004. It spread primarily through email attachments, tricking users into opening infected files. Once activated, it would replicate itself and send copies to contacts in the victim's address book, causing widespread damage to computer systems. The worm also had a notable feature: it launched a distributed denial-of-service (DDoS) attack against specific websites, including Microsoft. This made it one of the fastest-spreading worms at the time, leading to significant disruptions and financial losses for many organizations.