As if the recent weak earnings report and associated stock downturn weren't bad enough news for Zynga, at least five law firms are now actively investigating the social gaming powerhouse for security law violations related to sales of company stock three months ago.

Schubert, Jonckheer, & Kolbe, LLP; Johnson & Weaver, LLP; Bronstein, Gewirtz, & Grossman, LLC; Levi & Korsinsky; and Wohl & Fruchter, LLP have all announced they are actively investigating whether executives and shareholders including CEO Mark Pincus breached their fiduciary duty and broke securities law in selling over $500 million worth of stock in a secondary stock offering this April. In selling that stock at $12 a share—well above the current $3 share price brought on by the weak earnings report—the executives allegedly "misrepresented and/or failed to disclose materially adverse facts about its business and financial condition." In other words, they knew this was coming, and they sold their own interests rather than warning the general shareholders.

Besides CEO Mark Pincus, the list of major shareholders that sold off part of their interest in the company in April includes COO John Schappert and CFO Dave Wehner, venture capital firms Venture Partners, Silver Lake Partners, and Union Square Ventures, and even Google, which was revealed as an early Zynga investor during the latter company's IPO.

Simply selling the stock isn't proof of wrongdoing, of course—the law firms are going to have to prove that the sales came because of insider knowledge that the business was doing worse than it seemed to the outside world. It's hard to believe that the Zynga executives didn't have some inkling that their upcoming earnings report was going to come in well below expectations, but what they knew and when they knew it will be key to any legal ruling.

While Zynga hasn't technically been sued yet, the number of lawyers on the scent of this case makes it exceedingly likely that it will be the subject of a class-action lawsuit from its shareholders in the near future. That might be the best way that shareholders can get their voices heard on the matter—Zynga is somewhat notorious as one of the few companies where regular investors have next to no say in how the company is run.