Japan's Keio Corporation has confirmed a ransomware attack that disrupted business systems across parts of its group, while train services kept running normally. The company detected the attack in the early hours of September 26.

Keio runs one of Tokyo's major commuter rail networks along with retail, hotel and real-estate businesses. Japanese reports say credit card payments stopped working at some group stores and hotel reservation systems were hit, according to Japan Cyber Watch.

Train operations were unaffected because railway and corporate systems are kept on separate networks, the company said. It has cut off affected network connections and brought in outside cybersecurity experts to investigate the attack route and the damage.

Keio says it has not confirmed any leak of information so far. It is investigating whether business-confidential data or customer information was taken. Some reports say email addresses of nearly 60,000 members could be at risk, though the company has not confirmed this.

The incident has been reported to police. It shows how an attack on shared corporate systems can disrupt a company's wider business even when its transport services keep running.