Lockheed Martin on Saturday said it had suffered a " " cyberattack on May 21. The company, which is the largest U.S defense contractor, said it was forced to shut down remote access to deal with the attack, but maintained that no data was compromised.

Lockheed itself has offered few details about the breach. But Reuters, which first reported the intrusion last Thursday, cited unnamed sources as saying the compromise involved the use of cloned RSA SecurID tokens.

Wired on Wednesday L-3 is a major supplier of communication, intelligence, surveillance and reconnaissance technology to the Department of Defense.

Wired cited an internal email that it obtained from an L-3 employee warning that the company was actively targeted by attackers using cloned SecurID tokens. It's not clear from the email whether any intruders managed to break into L-3's networks, or were detected while they were attempting to do so.

L-3 did not immediately respond to a request for comment.