According to unnamed sources, the attackers managed to get into one of the U.S. government’s most sensitive computer networks, but it seems that protective measures allowed the breach to be quickly detected and blocked.
The White House Military Office (WHMO) "provides military support for White House functions, including food service, Presidential transportation, medical support and emergency medical services, and hospitality services," but also "oversees policy related to WHMO functions and Department of Defense assets" and "all military operations aboard Air Force One on Presidential missions worldwide," which includes communication with intelligence and military officials, as well as the communication of potential strategic nuclear commands.
The attack took place earlier last month, and came in the form of a spear phishing email to a White House employee.
"In this instance the attack was identified, the system was isolated, and there is no indication whatsoever that any exfiltration of data took place,” the unnamed official told the WFB.
Needless to say, a successful breach of this network would cause considerable strategic damage to the United States.
The attack has been traced back to Chinese servers, and officials believe that a group of Chinese cyber warfare specialists lead by a unit of the People’s Liberation Army might be behind it.
There's also speculations that the attack was due to the recent maritime dispute between Japan and China over a group of Japanese islands that the Chinese say belong to them. The fact that the U.S. has a defense treaty in place with Japan and has moved some of its Marine military units near the aforementioned islands might have triggered China's decision to target the WHMO.