Secret Service Special Agents (foreground) protecting the President of the United States in 2007.The Secret Service has primary jurisdiction over the prevention and investigation of counterfeiting of U.S. currency and U.S. treasury bonds notes. However, this agency is best known for their work protecting the President.
Today, the Secret Service is authorized by law to protect:
The president, the vice president, secretary of state (or other individuals next in order of succession to the Office of the President), the president-elect and vice president-elect.
The immediate families of the above individuals.
Former presidents and their spouses for their lifetimes, except when the spouse remarries. In 1997, Congressional legislation became effective limiting Secret Service protection to former presidents for a period of not more than 10 years from the date the former president leaves office.
Children of former presidents until age 16.
Former Vice Presidents six months after their term ends (the Secretary of Homeland Security can extend the protection time).
Families of former Vice Presidents six months after term ends.
Visiting heads of foreign states or governments and their spouses traveling with them, other distinguished foreign visitors to the United States, and official representatives of the United States performing special missions abroad.
Major presidential and vice presidential candidates, and their spouses within 120 days of a general presidential election.
Other individuals as designated per Executive Order of the President.
National Special Security Events, when designated as such by the Secretary of the Department of Homeland Security.
The Secret Service also investigates a wide variety of financial fraud crimes and identity theft and provides forensics assistance for some local crimes. The United States Secret Service Uniformed Division (UD) assists in the protection of foreign embassies, the United States Naval Observatory and the White House within Washington, D.C. Due to the discretion of this organization, many details about the Secret Service are currently classified.
http://en.wikipedia.org/wiki/United_States_Secret_Service