The lawsuit was presented in federal court in California last week, with Facebook pushing for an order that StudiVZ must stop mimicking the US firm's website and hand over any money it has made.

"This is a case to stop StudiVZ from operating a knockoff of Facebook," Facebook lawyers said. "A great part, if not all, of StudiVZ's success is due to copying and misuse of Facebook's intellectual property."

"We believe that our success thus far has been directly related to the unique look and feel of both the site and user interface, and are very disappointed that StudiVZ has unfairly used our creativity, innovation and effort by building a 'clone' site to compete directly against us," said deputy general counsel Mark Howitson. "Ultimately, we are supporters of innovation, not imitation."

Facebook unveiled a redesigned Web site Monday, July 21.

Denial

StudiVZ has denied the charge but asked for a declaratory judgment at the district court level in Stuttgart, Germany, reported DPA news agency.

The site was launched some 18 months after then Harvard University student Mark Zuckerberg brought Facebook to life in 2004 as a way to stay connected with the lives of college friends. The students who began the project later sold it to the Holtzbrinck group.

StudiVZ is gaining popularity and its creators have started localized versions in other parts of Europe, according to the lawsuit.

It has more than 10 million registered members in Germany, Austria and Switzerland - countries where Facebook has failed to gain the same level of success it enjoys in the United States.

Soaring popularity

In Germany alone, some 9 million web users have created profiles on online networks like StudiVZ or Facebook -- a 20 percent jump over a year ago, reported the industry association BITKOM in June.

The figures are based on data collected by the opinion research institute Forsa.

Viewed in terms of German citizens aged 14 and up, 12 percent have a profile in at least one of the communities. Among internet users in general the figure is roughly 17 percent.