Some 60 professors at public universities have been sent messages alleging their "secrets" were known and would be made public unless they paid money, the education ministry said Wednesday.
The ministry has sent warnings to about 200 organizations under its supervision, including universities and independent administrative agencies, urging them to ignore such blackmail attempts, officials said.
According to the Education, Culture, Sports, Science and Technology Ministry's personnel affairs division, the roughly 60 professors at 39 institutions received identical letters saying, "I have learned through an insider of your secret, which is deemed punishable by your institution. An investigation has been carried out, and I know everything about it."
The letters urged the recipients who wanted to have the "relevant documents" destroyed to deposit 500,000 yen into an account at a bank in Osaka by Thursday.
The letters were sent in envelopes listing a nonexistent return address in Chiyoda Ward, Tokyo. The sender's name was "Takuya Iwamoto," with the title "Planner" at the "Ethical Screening Measures Research Office."
The envelopes, posted in Osaka, were first reported to the ministry last Friday.