As Abercrombie & Fitch Co. prepares to expand to overseas markets, the casual youth retailer decided it wanted to tighten its grip on the legion of copies of its worn denim, striped polos and skinny tanks being sold around the globe.

The company hired a former agent from the FBI’s intellectual property unit to bolster the anti-counterfeiting efforts of its existing security operation — an example of a get-tough approach that some apparel companies are taking toward knockoffs.