Following the Civil War, counterfeit currency became such a rampant problem in the U.S. — more than a third of all bills were believed to be fakes — that the government was forced to act. In 1865, a special division of the Treasury Department was created to crack down on counterfeiting before it completely undermined the nation's economic system. That agency still fights bogus money today, but it's better known for its dark-suited agents and intimidating SUVs — it's the United States Secret Service, which also protects the President and other top political leaders. President Abraham Lincoln authorized the Secret Service on April 14, 1865 (ironically, the day he was assassinated at Ford's Theater); its mission expanded to full-time presidential protection following the assassination of President William McKinley in 1901. The 6,500-person agency was moved to the newly established Department of Homeland Security in 2002.