The U.S. Department of Health and Human Services has identified ambulance service as one of the biggest areas of overuse and abuse in Medicare -- companies billing millions for trips by patients who can walk, sit, stand or even drive their own cars. "It's a cash cow," said Assistant U.S. Attorney Beth Leahy, who prosecuted Penn Choice and five other ambulance fraud cases. "It's basically like a taxi service except an extremely expensive one that the taxpayers are financing." Penn Choice received $833,000 from Medicare in 2012, the year before it was indicted, according to the new data for the U.S. government health program for the elderly and disabled. The company went out of business after the indictment.