WASHINGTON - State Department employees snooped through the passport files of three presidential candidates Sens. Barack Obama, Hillary Rodham Clinton and John McCain and the department's inspector general is investigating.

State Department spokesman Sean McCormack said the violations of McCain and Clinton's passport files were not discovered until Friday, after officials were made aware of the unauthorized access of Obama's records and a separate search was conducted.

The incidents raise questions as to whether the information was accessed for political purposes and why two contractors involved in the Obama search were dismissed before investigators had a chance to interview them. It recalled an incident in 1992, when a Republican political appointee at the State Department was demoted over a search of presidential candidate Bill Clinton's passport records. At the time, Clinton was challenging President George H.W. Bush.