PLA Unit 61398

PLA Unit 61398 is the Military Unit Cover Designator (MUCD) of a People's Liberation Army advanced persistent threat unit that has been alleged to be the source of Chinese computer hacking attacks. Forensic evidence traces the base of operations to a 12-story building off Datong Road in a public, mixed-use area of Pudong in Shanghai. The group is also known by various other names including "Advanced Persistent Threat 1" ("APT1") and "Byzantine Candor", a codename given by US intelligence agencies since 2002.

A report by the computer security firm Mandiant stated that PLA Unit 61398 is believed to operate under the 2nd Bureau of the People's Liberation Army General Staff Department (GSD) Third Department Second Board (总参三部二局). and that there is evidence that it contains, or is itself, an entity Mandiant calls APT1, part of the advanced persistent threat that has attacked a broad range of corporations and government entities around the world since at least 2006. APT1 is described as comprising four large networks in Shanghai, two of which serve the Pudong New Area. It is one of more than 20 APT groups with origins in China. The Third and Fourth Department, responsible for electronic warfare, are believed to be comprise the PLA units mainly responsible for infiltrating and manipulating computer networks.

The group often compromises internal software "comment" features on legitimate web pages to infiltrate target computers that access the sites. The collective has stolen trade secrets and other confidential information from numerous foreign businesses and organizations over the course of seven years such as Lockheed Martin, Telvent, and other companies in the shipping, aeronautics, arms, energy, manufacturing, engineering, electronics, financial, and software sectors.

Dell SecureWorks says it believed the group includes the same group of attackers behind Operation Shady RAT, an extensive computer espionage campaign uncovered in 2011 in which more than 70 organizations over a five-year period, including the United Nations, government agencies in the United States, Canada, South Korea, Taiwan and Vietnam were targeted.

The attacks documented in the summer of 2011 represent a fragment of the Comment group's attacks, which go back at least to 2002, according to incident reports and investigators. FireEye, Inc. alone has tracked hundreds of targets in the last three years and estimates the group has attacked more than 1,000 organizations.

Most activity between malware embedded in a compromised system and the malware's controllers takes place during business hours in Beijing's time zone, suggesting that the group is professionally hired, rather than private hackers inspired by patriotic passions. The Unit is belived to be "staffed by perhaps thousands of people proficient in English as well as computer programming and network operations."

The government of China has consistently denied that it is involved in hacking. In response to the Mandiant Corporation report about Unit 61398, Hong Lei, a spokesperson for the Chinese foreign ministry, said such allegations were "irresponsible and unprofessional."