NEW YORK, (Reuters) – Recent cyber attacks on Google   and other American corporations have been traced to a top  Chinese university as well as a school with ties to the  Chinese military, the New York Times reported on Thursday,  citing people involved in the investigation.

Those people told the Times that the Chinese schools  involved are Shanghai Jiaotong University and the Lanxiang  Vocational School. They said the attacks may have started as  early as April 2009 — earlier than previously thought.

According to the report, investigators believe there is  evidence suggesting a link to a computer science class at the  vocational school taught by a Ukrainian professor. Google jolted U.S.-China ties with its Jan. 12 announcement  that it had faced a “highly sophisticated and targeted attack”  in mid-December, allegedly from inside China.

More than 20 other companies were also targeted, though  Google said a primary target was dissidents’ email accounts.

Jill Hazelbaker, Google’s director of corporate  communications said that the company’s investigation is  ongoing, but otherwise declined to comment.

The Chinese schools were not immediately available for  comment, but the Times said they had not heard that American  investigators had traced the Google attacks to their campuses.