Steam News has word that Call of Duty: Black Ops II is free to play on Valve's service until 4:00 pm EST Sunday. Here's word on the military first-person shooter sequel: "Pushing the boundaries of what fans have come to expect from the record-setting entertainment franchise, Call of Duty®: Black Ops II propels players into a near future, 21st Century Cold War, where technology and weapons have converged to create a new generation of warfare." The game is also on sale for the duration of the event for 33% off.