Google is everywhere. It gathers information to power its massive advertising arm. Google is tracking you around the internet, building an individual advertising profile to better serve you ads. Some users don’t mind, reasoning that if they’re going to see ads (advertising essentially powers the internet), they might as well see ones relevant to their interests.
The most intolerable thing is that you can’t modify your homepage back to the original one any more if your computer gets such virus. You might find some solution and uninstall it from control panel, but the virus just takes root there and you may find since your computer got such virus, it runs more and more slowly. Don’t wait for any longer time, otherwise your computer will be completely destroyed.