It comes as O2, Tesco Mobile and Sky Mobile customers across the United Kingdom experience problems with mobile data services.
"One of our third party suppliers has identified a global software issue in their system which has impacted us", it said.
It is not clear when the issue will be resolved, but O2 said it would share further updates as soon as possible.
The network also provides services to Sky, Tesco, Giffgaff and Lycamobile networks.
O2 has confirmed that the cause of the data issues appears to be a software issue linked to a 3rd party.
O2 said its technical teams are working with its supplier's teams to fix the problem.
O2 has said a "full service" will be restored by Friday morning following a data outage, which affected millions of users.
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"We'd encourage you to use Wi-Fi wherever you can and we are really sorry".
They said in a statement: "The network issue we are now experiencing remains a top priority for us and we are working as quickly as possible to fix the issues".
Local O2 customers have also reported issues, with many people in Dundee left unable to use data or make calls.
However, when the network was down for seven hours in 2015, the company did not offer compensation to all customers, instead saying payouts would be assessed on a "case-by-case" basis.
"The cause of today's network issue is in certain nodes in the core network resulting in network disturbances for a limited number of customers across the world, including in the United Kingdom", she said.
O2 did not say what is causing the fault.
A statement on their website said engineers are investigating issues related to data problems. The Register understands the Countdown service's SIMcards are on the O2 network as is the iBus system, which tracks the location of all of London's 7000+ buses.