(MCT) — WASHINGTON — A clandestine Chinese military unit has conducted sophisticated cyber espionage operations against dozens of American and Canadian companies, according to a private report that provides unusual new details about China’s involvement in cybertheft of economic and trade secrets.

The report by computer security firm Mandiant Corp. in Alexandria, Va., breaks new ground by attributing attacks against 141 companies to a specific 12-story office building in the financial center of Shanghai.