Facebook CEO Mark Zuckerberg announced Wednesday the Internet social network he started out of his college dorm room six years has reached 500 million active users around the world.

The much-expected milestone comes amid legal questions over ownership of the firm and a recent consumer survey that showed users aren’t thrilled with the Web site they’ve flocked to in recent years.

In a blog post, Zuckerberg thanked users and the company provided fresh statistics that show those users are spending lots more time on the site, producing content and visiting often. (Washington Post Co. Chairman Donald E. Graham is a member of Facebook’s board of directors.)

Here are some highlights:

Half of users get onto Facebook every day.

The average user has 130 friends.

A user on average posts photos, links to Web sites, posts videos and news stories or creates other content about 90 times each month.

1 million developers have created 550,000 Facebook apps.

Three out of 10 users access Facebook through their mobile phones and those users are twice as active as those who go onto the Web site on their PCs.

The milestone was announced in a blog post and is being accompanied by a Web campaign by the company for users to share their stories. Zuckerberg will be interviewed Wednesday by Diane Sawyer on World News Tonight.

But clouding the picture is a lawsuit by a New York businessman who claims Zuckerberg signed away a big chunk of the company to him before it became the half-billion-member sensation.

Facebook lawyer Lisa Simpson told Judge Richard Arcara, of the U.S. District Court of Buffalo, NY, that the company was “unsure at this moment” whether Zuckerberg signed a contract that purportedly entitles Paul Ceglia 84 percent of Facebook, according to Bloomberg.

At the time, Zuckerberg worked for Paul Ceglia as a software coder. The businessman filed a complaint against Facebook and Zuckerberg in state court in New York’s Allegany County on June 30. Ceglia claims that a contract he and Zuckerberg signed in April 2003 entitles him to ownership of most of the closely held company. Ceglia’s lawyer produced the document Tuesday at a hearing in federal court in Buffalo.

“Whether he signed this piece of paper, we’re unsure at this moment,” Simpson told U.S. District Judge Richard Arcara, according to Bloomberg.

Those comments, however, may be taken out of context, according to a source.

“Our intention was to indicate that plaintiff has not produced the original of the alleged agreement for anyone, including the court,” Facebook said in a statement.

“We have serious questions about the authenticity of the document and, assuming an original exists, we look forward to expressing our opinion about it once we see it.”