The Secret Service is best known for its primary public role: its agents protect the President of the United States. They also guard the President's family, the Vice President and his family, former Presidents, and Presidential candidates. They sometimes guard foreign dignitaries who are visiting the United States, especially foreign heads of state, and have been known to accompany American officials on diplomatic missions overseas.
Special Agents of the Secret Service don't wear uniforms, but the Secret Service also has two uniformed police agencies. There's the former White House Police (now known as the Secret Service Uniformed Division, since they currently guard foreign embassies in Washington, as well as the White House itself). And there's the uniformed Treasury Police Force.
The Secret Service has been charged by Congress with a number of little-known duties. They guard the precious metals in Treasury vaults. They guard the most valuable historical documents of the United States: originals of the Constitution, the Declaration of Independence, Lincoln's Second Inaugural Address, an American-owned copy of the Magna Carta, and so forth. Once they were assigned to guard the Mona Lisa, on her American tour in the 1960s.
The entire Secret Service is a division of the Treasury Department. Secret Service Special Agents (there are about 1,900 of them) are bodyguards for the President et al, but they all work for the Treasury. And the Treasury (through its divisions of the U.S. Mint and the Bureau of Engraving and Printing) prints the nation's money.
As Treasury police, the Secret Service guards the nation's currency; it is the only federal law enforcement agency with direct jurisdiction over counterfeiting and forgery. It analyzes documents for authenticity, and its fight against fake cash is still quite lively (especially since the skilled counterfeiters of Medellin, Columbia have gotten into the act). Government checks, bonds, and other obligations, which exist in untold millions and are worth untold billions, are common targets for forgery, which the Secret Service also battles. It even handles forgery of postage stamps.
But cash is fading in importance today as money has become electronic. As necessity beckoned, the Secret Service moved from fighting the counterfeiting of paper currency and the forging of checks, to the protection of funds transferred by wire.
From wire-fraud, it was a simple skip-and-jump to what is formally known as "access device fraud." Congress granted the Secret Service the authority to investigate "access device fraud" under Title 18 of the United States Code (U.S.C. Section 1029).
The term "access device" seems intuitively simple. It's some kind of high-tech gizmo you use to get money with. It makes good sense to put this sort of thing in the charge of counterfeiting and wire-fraud experts.
However, in Section 1029, the term "access device" is very generously defined. An access device is: "any card, plate, code, account number, or other means of account access that can be used, alone or in conjunction with another access device, to obtain money, goods, services, or any other thing of value, or that can be used to initiate a transfer of funds."
"Access device" can therefore be construed to include credit cards themselves (a popular forgery item nowadays). It also includes credit card account NUMBERS, those standards of the digital underground. The same goes for telephone charge cards (an increasingly popular item with telcos, who are tired of being robbed of pocket change by phone-booth thieves). And also telephone access CODES, those OTHER standards of the digital underground. (Stolen telephone codes may not "obtain money," but they certainly do obtain valuable "services," which is specifically forbidden by Section 1029.)