The Tokyo Chamber of Commerce and Industry said Wednesday hackers may have stolen the personal data of more than 12,000 people, most of them members of companies it represents.

The chamber said the names, home addresses and email addresses of people who took part in seminars it hosted may have been leaked in the breach. The loss did not include financial details such as bank account numbers, it said.

Police have launched an investigation. The chamber represents small and midsize businesses in Tokyo's 23 wards.

The announcement comes days after word of a massive data leak at the Japan Pension Service.

The latest hacking incident was confirmed on May 22, after an institution monitoring the organization's computer system detected suspicious activity. It was found that a staffer had opened an infected email attachment, which led to the attack.

The chamber had a total of 77,760 members as of the end of March. The members include companies and individuals running businesses.

Hideo Takano, an executive director with the chamber, apologized for the incident at a news conference in Tokyo.

Meanwhile, the Petroleum Association of Japan, an industry body comprising 14 major oil wholesalers and others, said its computers had been infected by a virus sent in an email attachment, but that no data leak had been confirmed.