Andrew knows ways to get into your system and find if you have been playing games. Here are some ways to hide that.
1) Put Games on a Flash Drive
2) Delete my Recent Documents (Must have hidden files visible)
3) *Most Useful* Go to Start Menu then click Run. In the text box type in RegEdit then click OK. This should open up a window. Open up the HKEY_CURRENT_USER list and then open up the SOFTWARE list in that list there should be history of All of the programs you have ever used. Delete the ones that are games *Note This will not delete your game , it will just delete any settings that you have set or saved data* One to definately delete would be Otaku Software (Deskspace).