Ericsson has admitted a fault in its network software has caused major mobile service outages in “multiple countries”. The company said the problem is thought to be due to an expired software certificate and it’s taken “immediate action” to minimize impact and support the restoration of services. A “limited number” of its network operator customers were affected, Ericsson said in a statement. These are thought to include O2 UK and Softbank in Japan.

Ericsson said it identified an issue in certain nodes in the core network resulting in network disturbances for customers using two specific software versions of the SGSN–MME (Serving GPRS Support Node – Mobility Management Entity). The company has decommissioned the faulty software and is helping the customers gradually restore services.

An initial root cause analysis indicates that the main issue was an expired certificate in the software versions installed with these customers, Ericsson said. A complete and comprehensive root cause analysis is still in progress.

Ericsson CEO Borje Ekholm apologised to the operator customers as well as their customers in a statement. “We work hard to ensure that our customers can limit the impact and restore their services as soon as possible,” he said.

O2 UK also issued an apology, after reports that millions of its customers were without service. The company said the issue affected data services mainly, while the additional demand on the network also led to some customers unable to make or receive calls.

Softbank managed to restore services after an over four-hour outage. The service disruption comes just days before it is set to price the IPO of its Japanese telecom business and contributed to a 5 percent fall in its share price on 06 December.