Lockheed Martin Corp, the U.S. government's No. 1 provider of information technology services, said on Sunday that a tenacious cyberattack on its network last weekend was part of a pattern of frequent attacks on it from around the world.

The fact is, in this new reality, we are a frequent target of adversaries around the world, Sondra Barbour, the company's chief information officer, said in a memorandum to employees.

Eight days after the significant and tenacious May 21 attack was detected and countered, Bethesda, Maryland-based Lockheed is still working around the clock to restore employee access to the network while maintaining the highest level of security, Barbour said.

The first response included proactively shutting down the company's virtual private network, she said. Other measures included resetting all user passwords, upgrading remote access SecurID tokens, and adding a new level of security to the remote access network log-on procedure, the memo said.

(Reporting by Jim Wolf; Editing by Chris Wilson)