On February 25th 2015 BitGo, the firm which "held" the recently liberated Bitfinex customer coins in a sort of deviant escrow demanded by the United States Commodity and Futures Trading Commision, published a blog post on how they were insured against theft. That blog post is no longer available on BitGo's website. Bitstamp reportedly also uses BitGo in a similar capacity though they assure customers that the particulars of their arrangement are so different this could never happen to their customers.

P2SH considered harmful, sorry for your loss.