CBS News has learned that a manhunt is underway for a traitor inside the Central Intelligence Agency.

The CIA and FBI are conducting a joint investigation into one of the worst security breaches in CIA history, which exposed thousands of top-secret documents that described CIA tools used to penetrate smart phones, smart televisions and computer systems.

Sources familiar with the investigation say it is looking for an insider — either a CIA employee or contractor — who had physical access to the material. The agency has not said publicly when the material was taken or how it was stolen.

Much of the material was classified and stored in a highly secure section of the intelligence agency, but sources say hundreds of people would have had access to the material. Investigators are going through those names.