An American cybersecurity firm has linked more than 100 cyber attacks on U.S. companies to to the Chinese government.

In a 60-page long document entitled APT1: Exposing One of China's Cyber Espionage Units,, the Virginia-based firm Mandiant traced 147 cases of corporate cyber espionage over a six-year period back to a group of hackers called the "Comment Crew," the New York Times reports.

The hackers drained hundreds of terabytes of data from companies like Coca-Cola, but also targeted firms with links to pipelines and power grids in the U.S., as well as computer security firms.

CNN reports that the activity can be traced to four networks near Shanghai -- with some operations taking place in a 12-story building that is also the headquarters of Unit 61398, a secret division of China's military.

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Officials at the Chinese embassy in Washington have denied any involvment, insisting that hacking is illegal under Chinese law: "Making baseless accusations based on premature analysis is irresponsible and unprofessional," Chinese foreign ministry spokesman Hong Lei said.

"China resolutely opposes any form of hacking activities," Lei said, adding that China was the victim of many cyberattacks -- most originating in the United States.