Office workers beware, or a snarky robot may unleash a barrage of ping pong balls upon you. A somewhat sinister individual from the CKBot group at UPenn's Modlab concocted the prank.
According to Bot Junkie, it operates as follows: "A remote control raises a cutout section of ceiling tile, and the robot fires ping pong balls down at the hapless human below. "
See for yourself. (Note: action begins around 1:50)