Washington, D.C. ? Food stamp recipients and retail stores illegally exchange hundreds of millions of dollars in benefits for cash instead of food, congressional investigators said Friday.

Known as trafficking, the practice has dropped sharply since the government switched from paper coupons to cards that work like debit cards. But trafficking still consumes $240 million a year, the Government Accountability Office said.

Typical offenders are small grocery and convenience stores, where the trafficking rate is more than 7 cents per dollar, while in large stores the rate is 0.2 cents per dollar, the report said.

Today, a penny of every dollar of benefits is trafficked, a rate that has declined from nearly 4 cents a decade ago, GAO said.