Early internet giant Yahoo has been hit with a £250,000 fine by the UK's data regulator over a breach which left details of half a billion users at risk after a Russian state-sponsored attack.

The fine comes after a 2014 cyber attack which left the details of millions of Yahoo account holders at risk. While there were 8 million UK Yahoo account holders, around 500,000 Brits were affected by the hack, while Sky email customers, which used Yahoo technology, were also affected.

The Information Commissioners Office, which issued the fine to Yahoo! UK Services Ltd, now part of US telecoms giant Verizon, said the company "failed to take appropriate technical and organisational measures to protect the data".

The ICO decision was reached earlier in May, shortly before a crackdown on European data rules as part of the new General Data Protection Regulation. Under the new laws, companies that suffer data breaches could be liable for fines of up to €20m (£17.5m), or 4pc of global turnover.

Yahoo blamed Russian hackers for the attack and last year the US government prosecuted two spies allegedly involved in the cyber attack.

"People expect that organisations will keep their personal data safe from malicious intruders who seek to exploit it," said ICO deputy operations commissioner James Dipple-Johnstone. "The failings our investigation identified are not what we expect from a company that had ample opportunity to implement appropriate measures, and potentially stop UK citizens’ data being compromised."