From CNet News:

The attackers typically lure people to the malicious sites by sending enticing e-mails and instant messages. When a victim clicks on a link, the computer becomes infected. In one case, a greeting card was displayed and a tune played in the background while spyware was being installed on the compromised PC,Websense said.

These sites are popping up in the blogosphere, taking advantage of the free hosting available at some of the free blogging sites. If you keep your malware detection software up to date and generally practice safe computing (don’t follow links in strange emails and IMs) you should be relatively safe.