Zynga is best known as the maker of FarmVille, Words With Friends and a host of other online games. And if the allegations in a new lawsuit prove true, the company's top brass certainly are playing by their own set of rules.

On Monday, the law firm Newman Ferrara filed a class action suit against Zynga, claiming that the company's executives acted on insider knowledge when, in April, they collectively sold off more than $500 million worth of company shares. (Hat tip to The Verge.)

Zynga's stock has since taken a beating. On Tuesday, the stock was trading at $2.93, a drop of almost 70 percent from its first-day share price of $9.50.

When Zynga first went public in December, employees were barred from selling their shares until May 28 -- a standard corporate procedure known as a stock lockup. But a handful of early investors and Zynga higher-ups, including CEO Mark Pincus, CFO Dave Wehner and COO John Schappert, were able to sell their shares in a secondary offering in early April.

But by the time the lockup period expired for the majority of Zynga employees, the stock was foundering badly. The executives and investors who'd sold off in April, however, escaped the worst of the damage.

Zynga declined to comment on the matter when reached by The Huffington Post.

The episode bears some resemblance to the dust-up over Facebook's IPO earlier this year. That stock debut was soon followed by more than a dozen shareholder lawsuits accusing the social-media giant of misleading the public about its outlook. Zynga's fortunes are closely related to Facebook's, since most people who play Zynga games do so through the social network.

The suit filed Monday claims that "Zynga misrepresented or failed to disclose material adverse facts" to the public, including the fact that it was "experiencing a rapid decline in user numbers and virtual goods sold in existing web games." By July, Zynga was publicly reporting weak second-quarter earnings and a poor outlook for the rest of 2012.

"While Zynga insiders were able to sell their holdings at $12 per share before Zynga’s second quarter financial results were announced, Zynga’s non-executive employees and other public shareholders suffered colossal losses on their investments," the suit reads in part. Zynga's lockup period expired about two months before the company announced its second-quarter earnings, giving employees and other shareholders enough time to dump their stock before the late-July earnings report drove prices even further down.

During a conference call last week, Pincus reportedly sidestepped the question of why he and other executives had sold off their stock in April, saying only that "we believe in the opportunity for social gaming and play to be a mass-market activity, as it is already becoming." At the time of the secondary offering, Zynga described it as an effort to "stagger" the company's unloading process so that the stock price wouldn't take a large one-day hit.

More insider-trading lawsuits are expected to appear in the next few days. Kotaku reports that at least four other law firms besides Newman Ferrara are conducting investigations into the company.

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