A worm is on the loose in Twitter messages, the same one that appeared early last month on the short message website.
If you click on a message that has the shortened UL "Goo.gl," which looks similar to Google, it will take you to a site that fakes a virus problem. If you then follow instructions, you'll install a malicious virus on your computer. You will be asked to pay to have it removed.
Twitter recommends if you see the Goo.gl link, change your password immediately.