Russian hackers have stolen 1.2bn usernames and passwords in a series of internet heists affecting 420,000 websites — in what is likely to be the biggest data breach ever recorded.

Russian hackers have stolen 1.2 billion user names and passwords in a series of Internet heists affecting 420,000 websites, according to a report.

A hacker secretly took over a computer server at the BBC and then launched a Christmas Day campaign to convince other cyber criminals to pay him for access to the system.