We've all got shameful gaming secrets. Three weeks solid spent playing EVE Online? 300 hours in Skyrim? Actually played through Aliens: Colonial Marines? You don't want someone seeing exactly how much time you've wasted while pretending to be working/ill/asleep/not in, do you?
In the gaming equivalent of 'Incognito Mode', Steam's latest beta client allows you to keep several games in your library hidden, while still allowing you to play them whenever you want.
As always with beta client updates you'll have to sign up to test it, which you can find out. It's not a perfect system yet either - you can only hide games on your own computer, and they'll still show up if you have a public profile, but it seems likely that Valve will add an option in for profile privacy at a later date.
You can check out the full details of the latest client update over on the Steam.