Shareholder litigation is typically brought under federal securities laws. In this case IBM misled the market by failing to disclose material adverse information which caused the stock price to fall. To prove you suffered losses you only have to show that you bought stock during the time period affected, and lost money as a result of the information coming to light.

This is interesting. Investors have a right to all material information about a company, and public companies are obligated to provide that information, and SEC regulations require that they do so. But, in this case, that information was classified, so IBM would be breaking the law by revealing it. Conflicting laws.

If the shareholders win, who knows, we may see more lawsuits like this. Maybe that would compel these companies to stand up to the government.