Excellent report and analysis of AIM pipeline worm
Social engineering is used, as always, to create an opportunity for infection. People, if somebody sends you a link via any IM client, please respond and say "did you send this?" *before* clicking on the link. It only takes a second, and may save you from an awful lot of grief (and save what's left of my non-grey hair - these infections can sometimes be damned difficult to get off a machine - prevention is always better than cure).