One of the more notorious rootkits of modern times is known as the TDSS rootkit family -
This rootkit has been around for a few years now but still springs up from time to time. If you are having issues with unauthorised Google redirects then this rootkit is one of a few possible culprits.
Luckily, Kaspersky have a useful tool for detecting and killing TDSS rootkits. Its free to use and if you are having any issue with redirects then I would recommend giving it a quick go, whether you have an antivirus program or internet security suite installed on your computer or not.
TDSS Killer is very easy to use as you can see in the video below:
In addition to TDSS, the tool may also be able to detect and neutralise other rootkits so it is well worth running a quick scan in order to find out if there are any surprises hiding on your PC.