By bizn_fun 
“We will co-operate fully with Ofcom throughout the investigation and apologise again for any issues caused by this incident,” they said.
Meanwhile, Three said it had “experienced disruption to voice services following an exceptional spike in network traffic triggered by a third-party software configuration change”.
“Since the outage, we have engaged openly with Ofcom and will continue to cooperate fully with their investigation,” it said.
According to Ofcom, firms must take proper action to identify risks and prepare for “anything that compromises the availability, performance or functionality of their network or service”.
It said providers must also prevent “adverse effects arising from any such compromises” – saying where this happens, they must take steps to mitigate them.
“The importance of connectivity cannot be underestimated,” said telecoms analyst Paolo Pescatore.
“We all demand a robust and reliable connection at home and out and about.”
He said outages can occur despite “significant efforts” to prevent them – but said there must be “a straightforward process to identify the issue and to learn lessons so it does not happen again”.