It's almost certainly a virus, might be the TDL3, a variant of the TDSS rootkit (also known as Alureon). It's exploiting a vulnerability in Java in order to write a small script into the Firefox folder which constantly redirects your search results to infected servers which may be constantly loading more and more crap onto your drives. Two ways to get around this, one is for Firefox users.
1. Navigate to: C:\\Program Files\\Mozilla Firefox\\extensions\\, look for a folder that is a string of letters, created around the time you began having the problem. Something like ''{BCB94CDD-5542-403F-9FB3-07D3DB1E9951}''
2. Open the folder, and then open the folder called ''chrome'', then ''content'', and look for a file inside called overlay.xul (variants may have different names).
3. Verify that it is the virus: does it have code similar to this: click to see code
4. If you have found the culprit, delete the file (or encrypt with Axcrypt which is reversible).
5. Replace it with a blank text file with the same name and extension.
6. Repeat the process â€" you may have multiple copies in multiple folders.
7. Test: Go back to Google, try your search results again.
Second way is to just use an anti-virus software. Try to use your own installed software, before trying the free ones below.
Ad-Aware Free
Spybot S & D
Hitman Pro