From the PokerAce FAQ:
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1. Is PokerAce Hud against the rules of the poker sites?

Answer: A lot of confusion has come from Party poker banning players because they used certain software after being warned not to. The software causing the problem were software that shared hand history information to a central server. PokerAce Hud uses your local PokerTracker database and to date, no poker site has had any problems with it and PokerStars even has it listed on its site as being OK to use.


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I didn't look any further.