McCaskill, the chairwoman of the Subcommittee on Contracting Oversight, said in a joint Senate Homeland Security subcommittee hearing on Thursday that USIS, a large contractor that does background checks on federal government employees, is being investigated for its alleged "systematic failure to conduct investigations."

The contractor conducted the security background check for Snowden. 

See The Hill's DEFCON Hill blog for more.

This post was updated at 4:50 p.m.