Games hosted in social networks, gaming servers or mobile phones can be used as massively parallel, but surreptitious processing networks. These grids, and the activities of the unwitting players, can be used for good (such as solving large resource allocation problems or finding improvised explosive devices) or for evil (to allow criminals to gain unauthorized access to a system or break encryption algorithms). Surreptitious processing networks differ from botnets in that no rouge processing elements are present on the user side; instead, the computational payload is outsourced to humans who unknowingly provide partial solutions as they play the game. This approach makes the solution of large computational problems and the recruitment and exploitation of participants easy. This department is part of a special issue on social networking.