Carphone Warehouse has been fined £400,000 following a cyber-attack in which more than three million customers' data was compromised.

The phone retailer's computer systems were hit in a cyber-attack when hackers gained access via out-of-date WordPress software.

Today the Information Commissioner's Office (ICO) has issued one of the largest fines in its history, after criticising the "systemic failures" of the company.

The incident, in 2015, allowed hackers to gain unauthorised access to the personal data of over three million customers and 1,000 employees.

The compromised customer data included names, addresses, phone numbers, dates of birth, marital statuses and – for about 18,000 customers – historical payment card details.

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What did the ICO investigation find?

Following an investigation, the ICO found multiple flaws in Carphone Warehouse's approach to data security and said the company had failed to take adequate steps to protect personal information.

Using valid login details, the hackers were able to access the system via out-of-date WordPress software.

The cyber-attack also exposed inadequacies in the organisation's technical security measures – parts of the software were out of date and the company failed to carry out routine security testing.

There were also inadequate measures in place to identify and delete historic data.

'The systemic failures related to rudimentary, commonplace measures'

Information Commissioner Elizabeth Denham said: "A company as large, well-resourced, and established as Carphone Warehouse should have been actively assessing its data security systems, and ensuring systems were robust and not vulnerable to such attacks.

"Carphone Warehouse should be at the top of its game when it comes to cybersecurity, and it is concerning that the systemic failures we found related to rudimentary, commonplace measures."

Carphone Warehouse said in a statement: "As the ICO notes in its report, we moved quickly at the time to secure our systems, to put in place additional security measures and to inform the ICO and potentially affected customers and colleagues. The ICO noted that there was no evidence of any individual data having been used by third parties.

"Since the attack in 2015 we have worked extensively with cybersecurity experts to improve and upgrade our security systems and processes.

"We are very sorry for any distress or inconvenience the incident may have caused."