Beijing, Feb 20 (IANS/EFE): The Chinese army is behind a series of cyberattacks on US companies and institutions, according to a study by a US computer security company.

A 60-page report released Tuesday by Mandiant says that a Shanghai-based group of hackers designated by the company as APT-1 "is likely government-sponsored and one of the most persistent of China's cyber threat actors".

APT-1 activities appear to coincide with those of People's Liberation Army Unit 61398, whose headquarters are in the Pudong district of Shanghai, Mandiant said.

Though the company has been unable to directly trace APT-1 hackers to the Unit 61398 building, it believes there can be no other explanation for why so many attacks are launched from the same, relatively small area.

The attacks have been on the rise for two years, according to Mandiant, adding that cyber-strikes on least 20 sectors have been identified, from military contractors to chemical plants and including telecommunications companies.

"Hacking attacks are transnational and anonymous. Determining their origins are extremely difficult. We don't know how the evidence in this so-called report can be tenable," a Chinese foreign ministry spokesman said Tuesday.

"Arbitrary criticism based on rudimentary data is irresponsible, unprofessional and not helpful in resolving the issue," Hong Lei said.