On the outskirts of Shanghai, in a run-down neighborhood dominated by a 12-story white office tower, sits a People’s Liberation Army base for China’s growing corps of cyberwarriors.

The building off Datong Road, surrounded by restaurants, massage parlors and a wine importer, is the headquarters of P.L.A. Unit 61398. A growing body of digital forensic evidence — confirmed by American intelligence officials who say they have tapped into the activity of the army unit for years — leaves little doubt that an overwhelming percentage of the attacks on American corporations, organizations and government agencies originate in and around the white tower.

One alleged hacker said the goal was to use the credit data to steal a million dollars – including, apparently, from individuals’ accounts – and give the money away as Christmas donations. Images posted online claimed to show the receipts.

A Twitter account tied to Anonymous posted a link to what they said was Stratfor’s tightly-guarded, confidential client list. Among those on the list: The US Army, the US Air Force and the Miami Police Department.