Imaut.b is an Internet worm that spreads through instant messages using the Yahoo! Messenger program. 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.b attempts to change the Internet Explorer default home page, disable the Task Manager and the Registry Editor and modify certain Yahoo! Messenger settings. However, due to bugs in its code the worm rarely succeds in harming the system.