Basically the mass amount of users playing DayZ ended up breaking Steam Authentication somehow, so steam servers for several games went completely down. DOTA for example has gone down because of the problems (supposedly. It may have actually been a Steam issue with DayZ being the main victim) caused by DayZ.
Lock On: Flaming Cliffs 2. Lets revitalize this game eh? http://www.youtube.com/watch?v=6FUge6ghaIo&hd=1