Twitter has been forced to take emergency action after a quarter of a million of its users had their accounts hacked.

Bosses at the social media website believe they've been targeted as part of a wider set of attacks aimed at US media companies.

The site says user names, email addresses and encrypted passwords may have been accessed during the attack.

Twitter has around 200 million active users.

Senior Editor at US technology website 'All Things Digital', Mike Isaac, says it's a small proportion of twitter users, but is still significant: