I would say that their email addresses have either been harvested for spamming, or that they may be infected by something that spreads via IM.
Tell your friends (and I'd do this yourself) to change their paswords to stronger ones, and aso check that their systems are clean.
Also, please use the modify button on the top right of your post, and de-activate your link. (change www to wXw) This will prevent others from potentially becoming infected, thanks.
-Scott-
