Weird Google redirects?

When I try to visit certain sites, many porn sites in particular, it redirects me to Google with a seemingly unrelated search term.

Just what the fuck is going on? It didn't used to do this, and it doesn't do it on my other computer. I figured it was some spyware nonsense, but after running Spybot and AdAware for the nth time, the problem persists.

It's keeping me from my porn, and that irritates me.

Halp?

http://www.kaspersky.com/
run complete scan in safe mode, or in normal mode too. also activate real-time protection.