[apefish]

Stars at least has had it laid out rather clearly for some time now.


With trivial exceptions, a player may play on only one account during a tournament and may not "hand off" his seat in mid-event to a different player. Violation of this rule may result in penalties ranging from a warning, to disqualification from the tournament (with partial or full forfeiture of winnings), to barring from PokerStars.

Examples:
You get a phone call during a PokerStars tournament. You ask your husband, who has already busted out of that tournament, to play your hands for you. You are on the phone for ten minutes and then resume play. This is permitted.
You and a friend are playing in the same tournament. You agree that if he busts out before you do, he will take over playing your account. This is prohibited.
You are playing in a tournament and lose power in your home due to a failure of your power station. You call a friend and he takes over until your power is returned. This is permitted.
Your husband is out of town for the weekend, but gives you his password. You log into both his account and yours and play both accounts in the same tournament. This is prohibited.
You have progressed to the final few tables of a tournament and somebody offers you cash equity for your seat. You allow the other player to sign into your account, or you continue to finish the tournament following the explicit instructions given by him. This is prohibited.