I want to start a Steam account and take advantage of some of the great deals they often have. I also want to be able to play certain games online legit without having to go through Garena or other similar third parties. Thing is, I still have certain games on my system, such as L4D, that, let's just say I didn't pay for. How much information does Steam retrieve from my PC? Would they detect unlicensed copies of games on my PC when using their site to purchase and play games?