"It’s the latest example of just how good scammers have become at manipulating Google search results. For months now, they’ve followed Google’s Trending Topics section and then used search engine optimization techniques to push hacked Web pages up to the top of Google’s search results, security experts say. They do this by flooding hacked pages with keywords that are then recorded by Google’s search engine.
Hackers have several ways of getting their code on legitimate Web sites — lately they’ve focused on stealing FTP login credentials, according to Dave Michmerhuizen, a research scientist with Barracuda Labs." – Content courtesy of Rogue antivirus lurks behind Google Doodle searches