Several Japanese companies and a university have reported separate data breaches and cyberattacks since Monday, potentially exposing personal information belonging to millions of customers, students, employees and other users.

Osaka Metropolitan University said on Monday that data belonging to at least 130,000 students and teachers may have been leaked after a suspected ransomware attack disrupted its information systems.

About 500 servers supporting the university's information systems stopped operating after the attack late last week, the university said. Its student campus network and faculty portal remained unavailable on Monday, forcing the cancellation of lectures.

Japanese discount retailer Mr. Max Holdings Ltd. said on Tuesday that personal data belonging to as many as 1.7 million customers may have been compromised after unauthorized access to a server supporting its online shopping services.

The company said it had suspended the affected services, blocked the route used in the attack and launched an investigation with external cybersecurity specialists, regulators and police. It is also strengthening its monitoring systems.

Internet services company GMO Research & AI Inc. said on Monday that up to 948,500 member records were stolen after unauthorized access to one of its servers.

The company said some members' reward points, worth about 2.9 million yen ($18,000), were illicitly exchanged for Amazon gift card codes.

Monogatari Corp., which operates the Yakiniku King barbecue restaurant chain, said on Monday that more than 10 million pieces of customer information had been leaked after unauthorized access to a system supporting its smartphone app for restaurant reservations and rewards.

The leaked information included email addresses and phone numbers and covered almost the company's entire registered user base, Monogatari said. It added that no misuse of the information had been confirmed.

Separately, Daiwa Securities Group Inc. said on Monday that information on about 110,000 customers of its securities brokerage unit, as well as other nonpersonal data, may have been compromised following unauthorized access to a server operated by one of its contractors.

Daiwa said the information, even if leaked, could not be used to conduct transactions, including online trades.

The incidents were reported separately by the organizations involved, and there was no indication in the information disclosed so far that they were connected to a common cyberattack.

The series of disclosures highlights the growing cybersecurity risks facing Japanese companies and institutions as they increasingly rely on online systems to manage customer, employee and student information. (ILKHA)