SHANGHAI - A tense stand-off between the United States and China over state-backed cyber espionage has dragged China's secretive hacking unit "61398" back into focus, after the military group was pinpointed last year for mounting cyber attacks on Western commercial targets.
US authorities on Monday charged five Chinese military officers at the unit, accusing them of hacking into American nuclear, metal and solar firms to steal trade secrets. China on Tuesday summoned the US ambassador in Beijing and warned it would retaliate if Washington followed through with the charges. It said the affair would damage "mutual trust".
At the centre of the row is a nondescript tower block in the northern suburbs of China's financial capital Shanghai, home to Chinese People's Liberation Army (PLA) Unit 61398.
The 12-storey block houses as many as several thousand staff, according to Mandiant, a US cyber security firm recently acquired by global network security company FireEye Inc. Mandiant identified the location as the source of a large number of espionage operations in a 70-page report last year.
"This unit is one of the most prolific. The group is really active and very aggressive," said Pierluigi Paganini, a cyber security expert and founder of Security Affairs, based in Italy.
Unit 61398's Shanghai base is kitted out with specialist fiber optic lines, while staff are trained in areas from English linguistics to covert communications, network security and cyber attack strategy, according to the Mandiant report.
The unit's operatives, working under code names such as "UglyGorilla", "DOTA" and "SuperHard", also have close research and recruitment ties with China's leading academic centers such as the prestigious Shanghai Jiaotong University.
Publicly available academic reports, school registers, recruitment notices and local online community notice boards show a web of social, educational and academic networks spreading out from the cyber spying unit. Military units in China are often organised in this way with schools, sports clubs and social events organised communally for unit members.