No Lag to Unplayable games


Jan 6, 2013
Hi, I built my computer about 2 weeks ago for gaming mainly. its been running fine since yesterday and all of a suddenly i only get about 10-20 fps (usually around 100-200)

My PC Specs:
Intel Core i5-3570K Processor
Gigabyte Nvidia GeForce GTX 660 Graphics Card
8GB Samsung DDR3 1600MHz RAM
128GB Samsung 830 Series SSD
1TB Seagate Barracuda Hard Drive

Running Windows 7

I will admit i pirated a couple programs, could i have got a virus? my computer is fast everywhere else except for gaming. if i did get a virus can you reccomend and free anti-virus?