In response to questions on Friday, Lockheed said in an e-mail that its computer experts had concluded that the breach at RSA in March was “a direct contributing factor” in the attack on its network. Government and industry officials said the hackers had used some of the RSA data and other techniques to piece together the coded password of a Lockheed contractor who had access to Lockheed’s system.

Image Harry Sverdlove, of Bit9, said RSA might need to reprogram many of its security tokens.

Lockheed, which makes fighter planes, spy satellites and other confidential equipment, said it had detected the attack quickly and blocked it before any important data was compromised.

Lockheed said it was replacing 45,000 SecurID tokens held by workers who need to log into its system from customer offices, hotels or their homes. It also required its employees to change their passwords, and it added a step to its sign-on process.

One top RSA official, who would speak only on the condition of anonymity on Friday because of customer relationships, acknowledged that some customers would lose confidence in the devices. “It’s certainly going to have an initial impact,” he said.

He said the company would discuss reprogramming tokens with companies. But, he said, in some cases that may require more work than other measures they could take to beef up different parts of their security systems.

RSA, based in Bedford, Mass., has declined to specify what data was stolen in March. It has also said that it detected the attack as the hackers were removing the data and that the attack was only partly successful.