"What's happening?" Twitter wants to know

Twitter used to ask "What are you doing?" No longer. The micro-blogging service now wants to know "What's happening?"

Twitter co-founder Biz Stone announced the change in Twitter's tag line in a blog post on Thursday.

"Twitter was originally conceived as a mobile status update service -- an easy way to keep in touch with people in your life by sending and receiving short, frequent answers to one question, 'What are you doing?'" Stone said.

But Twitter "has long outgrown the concept of personal status updates.

"People, organizations, and businesses quickly began leveraging the open nature of the network to share anything they wanted, completely ignoring the original question," he said.

"'What are you doing?' isn't the right question anymore," Stone said. "Starting today, we've shortened it by two characters. Twitter now asks, "What's happening?"

Stone said he did not expect the new question to change the way people use the service.

"We don't expect this to change how anyone uses Twitter, but maybe it'll make it easier to explain to your dad," he said.

Twitter, which allows users to pepper one another with 140-character-or-less messages known as "tweets," has grown rapidly in popularity since it was launched in August 2006 and has tens of millions of users.