April 4 (Bloomberg) -- Facebook Inc., the social-networking Web site, must defend against a lawsuit that accuses founder Mark Zuckerberg of stealing computer code, an appeals court ruled.

Yesterday's decision by the U.S. Court of Appeals in Boston revived a 2004 suit by ConnectU Inc. founders Cameron and Tyler Winklevoss that was dismissed last year on procedural grounds.

``Although the defendants have advanced other arguments, those arguments are either unavailing, or inadequately developed, or both,'' a three-judge panel wrote in the opinion.

The case may be joined with a second lawsuit by the Winklevosses that accuses Zuckerberg of copyright infringement, breach of contract, fraud and theft of trade secrets. ConnectU, based in Cambridge, Massachusetts, claims that code ultimately used for Facebook.com was developed by the brothers at Harvard University starting in 2003.

Zuckerberg has maintained that Facebook's code was developed independently. Facebook, based in Palo Alto, California, is the fifth-most trafficked Web site in the U.S. with 60 million users, according to court papers. It's battling News Corp.'s MySpace for advertising revenue that is expected to more than double to $900 million this year, research firm EMarketer Inc. estimates.

In a motion to dismiss the second lawsuit, Zuckerberg said ConnectU failed to prove that code for the competing sites was similar or that details such as Web page links were alike.

Facebook sued ConnectU last year in San Jose, California, accusing its rival of using Facebook member logins and passwords to gather information and lure them to the competing site. Both companies are closely held.

John F. Hornick, ConnectU's lawyer, didn't return a call for comment yesterday. A phone message left at Facebook's headquarters wasn't returned yesterday.

The cases are ConnectU LLC v. Zuckerberg, 04cv11923, and ConnectU Inc. v. Facebook Inc., 07cv10593, U.S. District Court, District of Massachusetts (Boston).

To contact the reporter on this story: Erik Larson in New York at elarson4@bloomberg.net.

Last Updated: April 4, 2008 00:01 EDT