Acxiom Corp. (Nasdaq:ACXM), Ambac Financial Group, Inc. (Nasdaq:AKT) and Jackson Hewitt Tax Service Inc. (Nasdaq:JTX) are among the biggest percentage losers in Thursday's trading among companies with market capitalizations under $1 billion.

Also included among the results: Alyst Acquisition Corp. (Nasdaq:AYA), Celldex Therapeutics Inc. (Nasdaq:CLDX), Encore Bancshares Inc. (Nasdaq:EBTX), Republic Airways Holdings Inc. (Nasdaq:RJET), Chemgenex Pharm Depository Receipt (Nasdaq:CXSP) and Old Second Bancorp Inc. (Nasdaq:OSBC).

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