Annunci.b is an Internet worm that propagates by e-mail through messages with infected attachments. Once the user opens such an attachment, the parasite secretly installs itself to the system and runs a spreading routine. It sends bogus letters to addresses it finds in the Windows Address Book. Then it runs a payload. Annunci.b connects the compromised computer to the Internet by dialing a high-cost phone number using a modem. It also blocks access to MSN Search, creates several shortcuts leading to infected files and opens undesirable web pages. The worm automatically runs on every Windows startup.