EMC Corp.'s security-systems unit RSA offered to swap the SecurID tokens it provides to clients such as defense contractors and government agencies after a network breach disclosed in March resulted in the theft of RSA data.

RSA will replace the tokens if the customer believes it is necessary, Helen Stefan, a spokeswoman, said in an interview. She said RSA has about 40 million tokens in use, providing clients' employees remote access to internal networks. Its defense-contractor clients include Lockheed Martin Corp., Northrop Grumman Corp. and Raytheon Co.

In March, Hopkinton, Massachusetts-based EMC said that a cyber attack resulted in information being taken from its systems, including data related to RSA's SecurID products. Bethesda, Maryland-based Lockheed Martin, the defense contractor that was the target of an attack on May 21, said last week the breach was the result of the data theft at RSA and that it would replace its security tokens.