A small Florida bank whose shares are so thinly traded that they are in danger of being delisted is suddenly one of the hottest stocks on the Nasdaq — and its president has no idea why.

Shares of OptimumBank Holdings (OPHC) in Fort Lauderdale have risen by roughly 450% this week, to $3.90 as of late Thursday afternoon. On most days few, if any, of its shares trade hands, but 1.7 million shares have been swapped this week, including nearly one million on Thursday alone.

The timing is particularly unusual because less then three weeks ago OptimumBank warned investors in a Securities and Exchange Commission filing that the stock was in danger of being delisted because it had been trading below $1 per share for at least 30 straight days. The company also faced delisting at one point last year because it did not hold the minimum amount of stockholder's equity for listing on the exchange. It regained compliance on that front after raising $8.6 million in a stock sale during the fourth quarter.

OptimumBank had no explanation for the sudden surge of interest in its shares and took the unusual of putting out a news release Thursday to quell any speculation. "The company is not aware of any material developments which could account for the recent unusual trading activity," OptimumBank said in a statement it attributed to President Richard L. Browdy.

Founded in 2000, OptimumBank has $154 million of assets and three branches in Broward County. The company reported a loss of $3.7 million in 2011, an improvement over the $8.5 million in lost in 2010, though it continues to operate with extremely high levels of problem loans. At Dec. 31, more than 30% of its loans were at least 90 days past due, according to Federal Deposit Insurance Corp. data.

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