At least a dozen U.S. National Security Agency employees have abused secret surveillance programs in the past decade, most often to spy on their significant others, according to the latest findings of the agency's internal watchdog.

In a letter to the Senate Judiciary Committee's top Republican, Charles Grassley, NSA Inspector General George Ellard outlined 12 instances of "intentional misuse" of the agency's intelligence gathering programs since January 1, 2003.

Grassley had asked the NSA internal watchdog to report on "intentional and willful" abuse of the NSA surveillance authority as public concerns mount over the vast scope of the U.S. government's spying program.