The U.S. government's biggest information technology provider Lockheed Martin Corp. (NYSE: LMT) is the latest to fall victim to hackers, with its computer systems being hit by a network security transgression.

The Bethesda, Maryland-based Lockheed Martin said it detected on May 21 a tenacious cyber-attack on its network, which was part of a pattern of frequent attacks on it from around the world.

The company said its information security team, which detected the attack almost immediately, took aggressive actions to protect all systems and data.

The initial actions taken by Lockheed Martin were to proactively shutdown the VPN network and implement an accelerated plan to strengthen its IT security.

These actions have included resetting all user passwords, upgrading the company's remote access SecurID tokens, and adding a new level of security to its remote access network log-on procedure, Lockheed Martin 's Chief Information Officer Sondra Barbour told employees through an internal memorandum.

As a result of the swift and deliberate actions taken to protect the network and increase IT security, our systems remain secure; no customer, program or employee personal data has been compromised, the company said in a statement.

Throughout the ongoing investigation, Lockheed Martin has continued to keep the appropriate U.S. government agencies informed of our actions. The team continues to work around the clock to restore employee access to the network, while maintaining the highest level of security, the company added.

Meanwhile, U.S. agencies offered assistance to Lockheed Martin. Cyber experts are now scouring the network to find any electronic DNA left behind by the hackers -- time-intensive work that may eventually help pinpoint the source of the attack, said one former senior government official.

The attack was fairly subtle but it underscored the growing information security challenges facing the U.S. government and industry, and validated Lockheed's ability to detect intrusions, Loren Thompson, a defense analyst who does consulting work for Lockheed and other military contractors, told Reuters.

In addition, the company's security officials said the disruptions in its systems might be linked to a attack on a vendor, which supplies coded security tokens to millions of users. The SecurID electronic tokens are supplied by the RSA Security division of the EMC Corp.

RSA bolstered security for clients, including Lockheed, after a network breach in March resulted in the theft of RSA data, Bloomberg reported citing a person familiar with the process.

EMC said the March cyber attack resulted in information being taken from its systems, including data related to RSA’s SecurID authentication products.

To counter the constant threats we face from adversaries around the world, we regularly take actions to increase the security of our systems and to protect our employee, customer and program data. Our policies, procedures and vigilance mitigate the cyber threats to our business, and we remain confident in the integrity of our robust, multi-layered information systems security, Lockheed Martin said in a statement.

Separately, Australia's government urged companies to tighten vigilance over cyber attacks launched offshore against some of the world's biggest resource firms and other businesses, warning high-tech threats were intensifying.

There is no doubt that cyber-security threats are becoming worse. Without talking about specific incidents, there have been a number of reports concerning our resource companies, Australian Attorney-General Robert McClelland told Reuters on the sidelines of a cyber security conference in Canberra.

Lockheed Martin stock closed Friday's regular trading up 0.35 percent at $77.26 on the NYSE.