The White House has confirmed that a spear-phishing attack struck an unclassified network in its environment, but says the affected system was identified and isolated.

The revelation came following a report Sunday by The Washington Free Beacon, a conservative online newspaper. According to the report, hackers broke into a system used by the White House Military Office, which provides military support for White House functions and includes units such as the Presidential Airlift Group and the White House Communications Agency. The attack reportedly occurred last month.

Sources cited in the report lay the blame for the attack on the doorstep of Chinese hackers, stating that it was likely the work of a Chinese cyberunit known as the 4th Department of General Staff of the People's Liberation Army, or 4PLA.

This incident is hardly the first time attackers from China have been accused of targeting U.S. government systems. In March, Gen. Keith Alexander, head of the U.S. Cyber Command, told the U.S. Senate Armed Services Committee that Chinese espionage was behind the March 2011 cyberattack against RSA, EMC's security division.

A White House official downplayed the recent attack in a statement to Dark Reading, however, noting that sensitive systems were not impacted.

"These types of attacks are not infrequent, and we have mitigation measures in place," the official says. "In this instance, the attack was identified, the system was isolated, and there is no indication whatsoever that any exfiltration of data took place. Moreover, there was never any impact or attempted breach of any classified system."

While the situation sounds scary, it should be viewed as business as usual for the most part, says Alex Cox, principal security researcher for the RSA FirstWatch Threat Research team.

"Government/defense, along with banking, is one of the most highly targeted verticals, and we see attacks like these on a daily basis across the industry," Cox explains. "The important part is that they are aware of them. The ones they miss are the ones to worry about, for obvious reasons."

The incident does, however, underscore the susceptibility of employees, even at the highest level of government, to targeting attacks, says Aaron Higbee, co-founder and CTO of PhishMe.

"In this case, we would like to think the White House Military Office has the most up-to-date hardware and antivirus software available to protect the nation's most critical information," he says. "But as we have seen time and time again, these attacks use the social engineering tactics of fear, curiosity, and urgency to lure users to open attachments, click URLs, or provide sensitive data to criminals -- truly, they are geared to help criminals establish an undetected presence within the White House network."

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