I often see threads in the various discussion forums online with people complaining that the Google search results look weird. They often complain the wrong sites come up, or they are full of ads or there are weird pop ups. The answer to these issues is often that their computers have been infected with some form of virus and/or malware.
Google has a specific FAQ page just to help people with this issue. You can find the page under the title Suspicious results and strange behavior: Strange pop-ups and other malware. If you have a similar issue, make sure to check out that page asap and take the necessary action to cleanse your computer.
As Google becomes more popular and less savvy searchers use computers and Google, more and more people get hit by these viruses. I believe this weekend had one of the higher levels of reports in the various forums, with complaints of this nature. Unsuspecting searchers, complaining that Google failed them, when in reality, their security software has failed them.