If you are usually downloading programs and entering P2P networks, it's good to be protected and Bitdefender is a really good choice.
It will protect our system against lots of virus, spyware, trojans, adware,... It doesn't affect the performance of your system, so you can install it and you won't notice it's running. Update it daily and keep your PC safe.
It's easy to use, just run it and let it erase any malware that could affect your PC. Don't hesitate, Bitdefender is one of the top antivirus you can find and it is totally free.