Waseda University said Monday it took about half a year before it discovered personal data on roughly 3,300 officials and students had leaked via cyberattacks.
Tokyo-based Waseda, one of the top private universities in Japan, said the stolen data included the names, identification numbers, email addresses and other information pertaining to officials and students.
A virus sent in an email disguised as a medical expense notification infected a computer Dec. 11 and later spread to several other computers, according to Waseda.
The infection was detected June 5 when Waseda was notified by an outside expert. It was caused by "an unknown type of virus," the university said.
The data theft follows a series of similar data leaks, including the recent leak of a massive amount of data from the Japan Pension Service.
"Recognizing the case is serious and grave, we are making all out efforts to probe the cause and prevent a recurrence," the university said in a statement.
Separately, Waseda also said the personal data of 14 people might have been stolen after it found its schedule management site was falsified via unauthorized access.