Twitter celebrates 140 million users on sixth birthday

Microblogging pioneer Twitter marked its sixth anniversary by announcing that it now has more than 140 million users.

The company said that its users average more than 340 million tweets daily, totalling upwards of 2 billion posts per week.

"When [Jack Dorsey] first sketched out his notion in March 2006, no one could have predicted the trajectory of this new communication tool," the company said in a blog post.

"Now it seems that there are as many ways to express yourself in 140 characters as there are people doing it."

The anniversary comes as Twitter finds itself facing an outlook that is both promising and fraught with danger.

Earlier this year, the company reinvested its revenues with a series of acquisitions that included aggregator service Summify and security specialist Dasient.

Like many other social networking sites, however, Twitter also finds itself a popular target for malware writers and online fraud operations.

Executives are being cautious in their plans to expand the service.

Earlier this year chief executive Dick Costolo said that the company would not be joining fellow social networking giant Facebook in offering shares on the stock market, opting instead to remain private and keep its finances out of the public record.