A problem with Ericsson software appears to be responsible for a huge O2 data outage.
Hours into a morning that saw around 30 million people unable to get 4G on their phones, it emerged that software made by the Swedish company appeared to be at fault.
The problems were also affecting Softbank in Japan and could be hitting other networks.
O2 had initially said only that the problem was the result of issues with a third-party supplier, and that its software had stopped working.
"Our teams are working closely with one of our third party suppliers who has identified an issue in their system which has impacted mobile services globally," it wrote in a tweet. "This is our top priority and we are really sorry."
Now Ericsson has said that it knows about the problems and that it will be resolved as soon as it can be.
“We are aware of the issue and are working together with our customers to solve it as soon as possible,” an Ericsson spokesman said.
Neither Ericsson or O2 have given any indication of when the problems might be fixed, despite repeated assurances that they are doing so as quickly as they can.
The outage has lasted for at least seven hours and there is little sign that the problem will be fixed imminently. It still appears to be affecting every customer of O2.
As well as the network's own users, customers of other carriers that rely on O2 – such as Tesco Mobile and GiffGaff – are also unable to get online.
O2 said the problem was affecting only internet connections, and some texts. But many customers said they have no signal at all, and calls are not getting through either.
The problems have also hit systems that seem entirely unrelated, such as live updating bus arrivals boards, which rely on O2's data network to report where they are.