We tried it and cheating happens, but for us it was bearable. We were running candidates through Codility as the very first level of screening (3 programming problems to be solved from home), then through 2 or 3 interviews. People were cheating on a test once in a while, but not badly enough to spoil the whole filtering process. At some point we started sending out a welcome e-mail before the screening session to make it clear that cheating is nothing more than a recipe for a seriously bad interview, that you really do not want to have. Helped somewhat, but still somebody cheats once in a while. I guess such is life.