Following network disturbances in a number of Ericsson’s customer networks, Ericsson identified a software glitch that was responsible for millions of smartphone users in Britain, Japan and other countries losing internet access on Thursday.

O2, Britain’s second biggest network, and Japan’s Softbank, both Ericsson customers, reported outages on their 4G networks earlier on Thursday.

Ericsson confirmed that a problem was in certain nodes in the core network using two specific software versions of the SGSN–MME (Serving GPRS Support Node – Mobility Management Entity). The software issue resulted in network disturbances "for a limited number" of Ericsson's customers in multiple countries, Ericsson said.

“The faulty software that has caused these issues is being decommissioned and we apologize not only to our customers but also to their customers. We work hard to ensure that our customers can limit the impact and restore their services as soon as possible," said Börje Ekholm, President and CEO, Ericsson.

Ericsson said that an initial root cause analysis indicates that the main issue was an expired certificate in some software versions.

The company says it has already restored most of the affected customers’ network services.

O2, which is owned by Spain’s Telefonica, said customers of Tesco Mobile, Sky Mobile and GiffGaff, which all use its network, were affected by the outage.

O2 chief executive Mark Evans said his teams were working hard with Ericsson to find a swift solution.