Imaut.u is an Internet worm that spreads through instant messages using AIM, Yahoo! Messenger 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.u changes the Internet Explorer default home page, disables the Task Manager and the Registry Editor and modifies certain Yahoo! Messenger settings. It also attempts to open malicious web sites and change security settings of instant messaging programs. Furthermore, it can terminate running security-related processes. The parasite runs on every Windows startup.