Imaut is an Internet worm that spreads through instant messages using Yahoo! Messenger, AIM and Windows Live Messenger programs. The parasite’s messages contain links to malicious web pages. Once the user clicks on such a link, the worm gets secretly downloaded and installed to the system. Then it runs a spreading routine and a payload. Imaut changes the Internet Explorer default home page, disables the Task Manager and the Registry Editor, terminates some antivirus programs and modifies certain Yahoo! Messenger settings. The worm is able to update itself via the Internet. It automatically runs on every Windows startup.