A stash of 2,000 documents smuggled out of the former USSR is now available for viewing at Cambridge University. As intelligence historian Christian Andrew told Time, the documents represent "the most important single intelligence source ever," listing the names of around 1,000 spies who operated in the U.S., designs for various booby traps and weapons and plots that were later given names such as "the Mousetrap."

The documents have been held in secret since Vasili Mitrokhin, a former KGB official-turned-dissident, snuck them out of the collapsed Soviet Union in 1992. Mitrokhin first tried bringing them to a U.S. embassy in Latvia. (Time writes that the Americans turned him away; the Guardian states that it was actually the long lines at the embassy that deterred him.) He next tried the British embassy, which was more receptive. Mitrokhin was taken to Britain to continue life under a new name and identity, and since then the classified documents have been stashed in 19 boxes at an archive in Cambridge, Time writes.

Over the years, the papers have proven especially useful for identifying former spies and for offering insight into some of the USSR's troubles with its embedded intelligence officers. One British spy who was recruited to work for the Soviets was “constantly under the influence of alcohol,” while another was “not very good at keeping secrets,” Time reports.

In 1999, Mitrokhin published a book revealing the names of various spies, including Melita Norwood, and 87-year-old grandmother who had given the Soviets information about the U.K.'s nuclear research, Time reports. In another case, an NSA employee named Robert Lipka was revealed as having sold the Soviets secrets back in the 1960s, leading to his belated arrest and sentencing of 18 years in prison.

In some cases, however, the claims contained in the secret files might themselves be propaganda. As the Guardian writes, "intelligence analysts and some Soviet defectors have warned that the KGB seriously exaggerated the significance and number of its contacts and operations to impress the Soviet leadership – and increase its budget."

Those interested in getting a first-hand look at Mitrokhin's typed translations (the original handwritten notes he smuggled out while on the job are still classified) can inquire at Cambridge's Churchill Archives Center.