Redirected to Bogus Search Engines

[KDXXX]

When I do a google search and click on a link I get redirected to sites like Premium Link Upgrade or monstersearch.com . Sometimes I get redirected to those URL's but the page displayed could be a porn site. If you click on the thumbnail it opens another bogus search engine link or a google search with various sex themes. However if you change the URL to the address of the actual site clicking on the link will take you (most of the time) to the gallery.

Is this a virus, spyware? I did all the scans but this is getting out of hand.

Thanks!