The worm is IM.GiftCom.All. The worm attempts to dupe IM users making them think that an acquaintance has sent them a link to a harmless Santa Claus file . Once you click on the file , you will see an image of Santa, but what you don't notice is that a rootkit being installed on their system. A rootkit is a tool designed to hide processes and files from the security software used to lock down control of a computer after an initial hack. The malicious attacker can then distribute messages to the user's IM contacts, using a similar technique to lure the unsuspecting acquaintance to click on the link and the worm keeps spreading .
Not only this , there are other worms on IM networks that spread rapidly. They appear as a message from a buddy with a link that looks innocent, but in fact points to malicious code somewhere on the Internet. Once the user clicks on the link, malicious code is installed and runs on the computer. The worm then spreads itself by sending messages to all names on the victim's contact list.These can be treated as medium level security threats .