Most poker players know better than to do this. Yesterday, a really good player I know was deep in a $3 rebuy tourney at pokerstars when he began to experience internet problems. He panicked and called a buddy. He gave his buddy his password and then his buddy played on his account for 15 minutes while he got his connection problem fixed. Pokerstars security picked up on this and now his account is shut down and I don't think they will let him back to play again.