Chances are you've heard the term rehypothecation. It refers to the practice by broker dealers of using the cash collateral posted by trading partners for its own purposes. Obviously, these are funds that are supposed to collateralize a trade, providing a cushion should the trading partner not be able to live up to terms.

A Reuters columnist takes issue with the practice: "There's nothing wrong with a dealer taking legitimate steps to insure an orderly unwind of a busted trade. But Wall Street firms should not have free license to reuse this collateral any way they see fit. The Obama administration should revise its proposal to require derivatives dealers to hold all cash collateral in segregated escrow accounts that can't be reused or touched by the dealer." We'll see if this develops legs as an issue. There are so many it may well fall by the wayside.  

For more:
- here's the column

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