Three Mobile has come under fire for failing to inform customers that their data had fallen victim to a security breach.

The Telegraph revealed that cyber criminals had accessed customers' personal details, including their name, phone number, phone type, date of birth, address, marital status, previous address, gender, employment status and email address.

Many customers are now complaining that the UK network failed to inform them of the incident and that they only learned of the attack from the media.

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Three admitted that cyber attackers had accessed the data of some customers who were due an upgrade and that this number totalled 133,827.

The company initially responded to queries on social media before posting a statement to its website which contained a customer service number.

But many customers weren't happy about how long it took Three to provide customers with information, saying that social media wasn't the way to announce such a major breach.

This content is imported from Twitter. You may be able to find the same content in another format, or you may be able to find more information, at their web site. @ThreeUK appalled - no communication from Three about data breach. Got everything from the press. #unacceptable — John Conry (@jconry) November 18, 2016

The National Crime Agency has arrested three people in connection with the incident, two on suspicion of computer misuse offences and one on suspicion of attempting to pervert the course of justice.

Three says it has now started contacting the affected customers and increased security.

This content is imported from Twitter. You may be able to find the same content in another format, or you may be able to find more information, at their web site. Please see a statement from our CEO David Dyson regarding recent fraudulent activity, affecting some Three customers https://t.co/wbxyoRNCol — Three UK (@ThreeUK) November 18, 2016

David Dyson, Three's chief executive, has apologised for causing "concern and inconvenience".

"We are now contacting all of these customers today to individually confirm what information has been accessed and directly answer any questions they have," he said.

"We believe the primary purpose of this was not to steal customer information but was criminal activity to acquire new handsets fraudulently."

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