So the spammers seems to have another possibility to infest Windows pcs:

URL redirect notifications are often meant to serve as security measures, but at least one malware blackhat is exploiting these services and redirecting site visitors from the website they think they are about to visit to a spyware-infested haven. That’s bad enough on its own, but the as-yet-unknown assailant has also used search engine optimizations to push the polluted redirectors higher in Google’s search rankings.
[From ArsTechnica – URL redirects open scareware loophole at major sites]

I see the potential for having problems when a PC user visits his friends’ MySpace, Facebook or similar pages, where there’s a high traffic volumen and he might not except to be in danger…

Once again, Mac users seems to have less reason to be concerned as any installation of whatsoever that modifies the system installation as such, is always confirmed by the user.