An investigation was under way today into how Twitter social networking website was infected by a computer "worm" sent by a rival over the weekend, its co-founder Biz Stone said.

Mr Stone said in his blog that Twitter suffered four attacks from a programme known as a worm starting on Saturday and ending early yesterday.

The bug was set up to promote an alternative social networking site, StalkDaily.com, and was designed to reproduce itself automatically once clicked on.

It displayed Twitter messages, known as "tweets", on affected accounts, urging people to visit the rival website. Nearly 10,000 unwanted tweets had to be deleted to contain the potential damage.

Mr Stone reassured Twitter users that no personal information was stolen.

He wrote: "On a weekend normally reserved for bunnies, a worm took centre stage. We are still reviewing all the details, cleaning up, and we remain on alert. We will conduct a full review of the weekend activities. Everything from how it happened, how we reacted, and preventative measures will be covered."

The 17-year-old founder of StalkDaily.com, Michael Mooney, admitted creating the malicious worm. The high school student from Brooklyn said he wanted to promote his website at the same time as exposing Twitter's weaknesses.

"I really didn't think it was going to get that much attention, but then I started to see all these stories about it and thought, 'Oh my God'," he said.