SAN FRANCISCO (AP) — A nettlesome computer program that tormented Twitter over the weekend is another reminder of the challenges facing the rapidly growing online communications service.

The mischievous program, known as a “worm,” targeted Twitter’s network with four different attacks starting early Saturday and ending early Monday, according to Twitter co-founder Biz Stone.

The worm was a potentially malicious program designed to automatically reproduce itself once it’s clicked on. But Stone says it didn’t filch any personal information from the more than 6 million people with Twitter accounts.