Bosses at the social media networking website were forced to reset accounts after a major security loophole was uncovered.That meant celebrities such as Oprah Winfrey, who has built up a massive list of 3.5 million followers, were left with no followers at all.

The bug allowed Twitter users to force a celebrity to follow them. That would also have opened up high profile users to spammers and abusive messages. Twitter was forced to wipe people's accounts to fix the problem.

"We identified and resolved a bug that permitted a user to 'force' other users to follow them," the social networking site said. "We're now working to rollback all abuse of the bug that took place."

Blackberry phone maker Research in Motion kept the number one spot, with a 36% smartphone market share.

Google Android phones accounted for 28% of sales and iPhones for 21% in the first three months of the year.

The leading brand shake-up is the latest sign of increasing competition in the fast-growing market for smartphones, which allow users to browse the web, send emails and run specialised applications.

Last month, Hewlett-Packard Co announced it would pay £800m to acquire Palm, which sells two smartphone models based on its WebOS operating system.

Microsoft, whose Windows operating system is used in the majority of the world's PCs, unveiled a pair of smartphones last month and recently launched a revamped version of its mobile operating system.