Shares of FirstFed Financial Corp. jumped more than 33 percent on Thursday after a Wall Street analyst questioned whether so-called naked short-selling might be taking place, since short interest in the company has exceeded the number of publicly traded shares.

Keefe Bruyette & Woods analyst Frederick Cannon said short interest in the Los Angeles-based parent of First Federal Bank of California increased to 93 percent of outstanding shares and 108 percent of the reported public float of 11.7 million shares on Aug. 12, according to the most recently available figures.

"We question whether or not this level of shares has actually been borrowed and sold short under stock exchange rules," Cannon said in a note to investors. "Further, this may raise the possibility of a New York Stock Exchange or Securities and Exchange Commission review of the short positions in the company."

Short-sellers, betting that a stock's price will fall, borrow shares and sell them. If the price drops as expected, they buy cheaper shares to replace the borrowed ones and pocket the difference as profit. Naked short-selling takes place when sellers don't actually borrow the shares before selling them, and then have to cover positions immediately after the sale.

A temporary order from the SEC banning naked short-selling of certain financial stocks expired on Aug. 12.

A week after that expiration, FirstFed reported news that significantly improved its stock price. Shares shot up 30 percent after bank said it not only had reduced its exposure to troublesome adjustable-rate loans and mortgage-backed securities, but had seen a drop in single-family home loan delinquencies in July.

FirstFed shares closed up $4.03, or 34 percent, to $16.02 in Thursday trading on the New York Stock Exchange. Shares are still down 56 percent from the first of this year.

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