• by Wendy Davis , April 16, 2010

Continuing its campaign to stem the sale of its gaming currency on outside sites, Zynga has sued the auction site PlayerAuctions.com for allegedly enabling people to sell virtual products.

In a complaint filed recently in U.S. District Court in the central district of California, the social gaming site alleges that PlayerAuctions.com unlawfully allows people to advertise and sell virtual currency used in games like "Mafia Wars," "Farmville," and "Yoville."

"Zynga has not authorized any third party to sell the 'virtual currency' or 'virtual goods' required to play the games," the company argues. Zynga adds that its terms of service bar users from selling virtual products outside of the game.

Zynga argues that its trademark is infringed by PlayerAuctions because the auction site allegedly uses the game names to advertise sales of currency. Zynga also alleges copyright infringement, on the theory that images from its games are used on PlayerAuctions. In addition, Zynga alleges that PlayerAuctions has interfered with the user agreement between Zynga and gamers.

Zynga has brought several other cases against companies who have allegedly violated its copyright and trademark by selling gaming currency. But this latest lawsuit is somewhat different from the prior ones because PlayerAuctions allegedly only provides a platform that allows users to sell the products.

The gaming company drew notoriety last year for allegedly displaying questionable ads in its games. Last November, TechCrunch posted a video of Zynga CEO Mark Pincus admitting that he "did every horrible thing in the book" to grow revenues.

Zynga currently is defending itself in a lawsuit alleging that the company helped to create "highly misleading" ads. That case, a potential class-action, was brought by California resident Rebecca Swift, who alleges that she lost about $200 as a result of misleading ads.