The three founders of ConnectU are suing Mark Zuckerberg for fraud, copyright infringement and misappropriation of trade secrets. The action asks the court to shut Facebook and give control of the company and its assets to ConnectU's founders. Facebook has responded by asking a judge to dismiss the lawsuit. A hearing is being held in Boston.

Facebook started in 2004, a few months before ConnectU went online, and now has 31 million users, compared with about 70,000 users for ConnectU, based in Greenwich, Connecticut. Last year, Facebook turned down a £500 million buyout offer from Yahoo.

A spokeswoman for Facebook, based in Palo Alto, California, declined to comment. But in court filings, Facebook's lawyers say ConnectU has no evidence for "broad-brush allegations" against Zuckerberg, and deny he pilfered his ideas for Facebook from his fellow Harvard students.

"Each of them had different interests and activities," they wrote. "Only one of them had an idea significant enough to build a great company. That one person was Mark Zuckerberg."

Facebook and ConnectU connect college students and others online. Both allow users to post profiles with pictures, biographies and other personal information and create extended networks of people at their schools or jobs or with similar interests.

ConnectU originally filed suit in 2004, but it was dismissed on a technicality and immediately refiled. The lawsuit claims that in December 2002, ConnectU founders Cameron and Tyler Winklevoss - who are brothers - and Divya Narendra began to develop a social networking site for the Harvard community called Harvard Connection.

In November 2003, the three asked Zuckerberg to complete software and database work on the site. They repeatedly asked him to finish before they graduated in June 2004, and Zuckerberg assured them he was working hard to complete it, the lawsuit says.

"Such statements were false and Zuckerberg never intended to provide the code and instead intended to breach his promise ... and intended to steal the idea for the Harvard Connection website, and in fact he did so," the suit alleges.

Zuckerberg launched Thefacebook.com in February 2004. ConnectU started its website in May of that year. By beating ConnectU to the market, Facebook gained a huge advantage, the lawsuit claims.