Today at Facebook's developer's conference, social games widgetmaker Zynga will announce a $29 million round of funding — the company's second — led by Kleiner Perkins, the VC firm that backed Amazon.com and Google. Zynga has also acquired virtual world app YoVille and added former Electronic Arts creative exec Bing Gordon to its board. The company makes games like Poker and Attack, a Risk clone, for Facebook and other social networks. Zynga founder Mark Pincus told the Wall Street Journal that Zynga has 18 million monthly visitors and adds another 450,000 users a day. Kleiner Perkins partner John Doeer said his firm went ahead with the Zynga deal because of that kind of growth, telling the Journal Zynga has "cracked the code" on how to develop games that go viral fast. But really, how Zynga adds new users isn't all that complicated, clever or sustainable.

Zynga makes its games easier to win for users who successfully spam their friends into signing up to play. See the above image for how Zynga does this with Attack, its version of world-concquering game Risk. The problem for Zynga and its new investors: The executives who run Facebook's platform don't like this kind of viral growth. In a blog post Monday, Facebook's Paul Jeffries explained:

Facebook is about empowering and connecting people through the sharing of information. That's undermined if users who receive an invitation or other communication suspect it was sent for an ulterior motive, such as gaining points in a game.

Yesterday, Jeffries' thoughts became rules for the Facebook platform. According to Inside Facebook,

Applications are no longer allowed to "create artificial or inappropriate incentives to use Facebook features (including, for example, sending requests and adding profile boxes).

In the past few weeks, Facebook has temporarily banned apps by top widgetmakers Rock You and Slide, and has punished other popular app makers too, making it clear that widgetmakers which break Facebook's ever-changing platform rules — "crack its code," so to speak — don't get away with it anymore.

That is, unless they're announcing funding from Kleiner Perkins on a day dedicated to convincing Facebook developers that such a sweet deal could happen for them, too.