From the _New Oxford American Dictionary_:

> For complex historical reasons, prove developed two past participles: proved and proven. Both are correct and can be used more or less interchangeably: _this hasn't been proved yet_; _this hasn't been proven yet_. _Proven_ is the more common form when used as an adjective before the noun it modifies: _a proven talent (not _a proved talent_). Otherwise, the choice between _proved_ and _proven_ is not a matter of correctness, but usually of sound and rhythm—and often, consequently, a matter of familiarity, as in the legal idiom _innocent until proven guilty_.