BERLIN (REUTERS) - German rail operator Deutsche Bahn said on Saturday (May 13) its systems were infected by a global cyber attack that caused computer turmoil in nearly 100 countries.

It said in a statement that train services were not disrupted but some electronic boards at stations announcing arrivals and departures had been affected.

Pictures posted online by travellers showed red windows appearing on announcement boards with a message demanding a cash payment to restore access. Deutsche Bahn said it was working to rectify the problem.

German Interior Minister Thomas de Maiziere said government computer systems were not affected.

The cyber attack hit international shipper FedEx and disrupted Britain's health care system. Researchers at security software maker Avast said they had observed 57,000 infections in 99 countries with Russia, Ukraine and Taiwan the top targets.

Cyber extortionists used ransomware to encrypt data on the computers, demanding payments of US$300 (S$420) to US$600 (S$841) to restore access.

Victims were tricked into opening malicious malware attachments to spam emails that appeared to contain invoices, job offers, security warnings and other legitimate files.

The most disruptive attacks were reported in Britain, where hospitals and clinics were forced to turn away patients after losing access to computers.