The U.S. GAO's 2010 findings regarding the great difficulty of accurately gauging the economic impact of copyright infringement was reinforced within the same report by the body's research into three commonly cited estimates that had previously been provided to U.S. agencies. The GAO report explained that the sources a Federal Bureau of Investigation (FBI) estimate, a Customs and Border Protection (CBP) press release and a Motor and Equipment Manufacturers Association estimate "cannot be substantiated or traced back to an underlying data source or methodology."

Answer this question, if possible (if impossible, reply "unanswerable"): What did the FBI use as a source?
estimate