Experian, the FTSE 100 credit monitoring group, suffered its biggest one-day fall in more than a year after the personal details of up to 15 million T-Mobile US customers were stolen in a data breach.

The hack, which lost data provided by potential mobile customers as part of standard credit checks, led to scathing criticism from T-Mobile boss John Legere. “I am incredibly angry about this data breach and we will institute a thorough review of our relationship with Experian,” he said.

Mr Legere said he was “working as fast as possible to provide alternate protection options”. There have been a rising number of cyber attacks in the past two years leading to high-profile breaches of security at Sony, Staples, Target and Home Depot in the US. – Copyright The Financial Times Limited 2015