Security experts said companies in many industries had increased network monitoring or changed passwords and PINs for the tokens since the RSA breach.

But some of the specialists said that until more details were known, it remained possible that the attempted intrusion at Lockheed was not tied to the RSA breach.

The RSA tokens provide security beyond a user name or password by requiring users to append a unique number generated by the token each time they connect to their corporate or government networks.

Soon after the breach in March, RSA’s chairman, Art Coviello, said the company’s investigation had revealed that the intruder successfully stole digital information from the company that was related to RSA’s SecurID products.

He did not give precise details about the nature of the information but said it could potentially reduce the effectiveness of the system in the face of a “broader attack.” The company said then that there was no indication that the information had been used to attack its customers.

Some computer security specialists said at the time that the compromised information was a file of master keys — long numbers — that are a part of the RSA encryption system. If the intruder did gain those numbers, it would make it possible to fashion an attack based on independently generating the keys used by individual customers.

RSA officials have said that the intrusion was only partly successful.

Mr. Lewis, the security specialist at the Center for Strategic and International Studies, said the intruders had been detected as they were trying to transfer data by security software provided by the NetWitness Corporation, a company that provides network monitoring software. In April, NetWitness was acquired by RSA’s parent company, EMC.