By Arshad Mohammed and Joseph Menn, Jun. 15, 2015, Reuters

WASHINGTON (Reuters) - When a retired 51-year-old military man disclosed in a U.S. security clearance application that he had a 20-year affair with his former college roommate's wife, it was supposed to remain a secret between him and the government.

The disclosure last week that hackers had penetrated a database containing such intimate and possibly damaging facts about millions of government and private employees has shaken Washington.

The hacking of the White House Office of Personnel Management (OPM) could provide a treasure trove for foreign spies.

The military man's affair, divulged when he got a job with a defense contractor and applied to upgrade his clearance, is just one example of the extensive potential for disruption, embarrassment and even blackmail arising from the hacking.

The man had kept the affair secret from his wife for two decades before disclosing it on the government's innocuously named Standard Form 86 (SF 86), filled out by millions of Americans seeking security clearances.