Class action lawsuit brought against Zynga
Zynga has yet to provide a response to the class-action lawsuit, but Facebook has come into the fray, calling the lawsuit "frivolous," as the ads come from a third-party service. This is true, as the lawsuit is undoubtedly over the Offerpal service, which Zynga dumped after it became apparent that users were being taken in by the scam-like behavior of different offers and that in order to go public, they would have to brush it under the rug. For those that do not know about trial/offer-based services, here's the low-down: they give you incentives to visit ads and participate in different trials or subscriptions to get microtransaction money in different games or sites. Offerpal is one of these, with TrialPay being another big name (as well as one used by Zynga's main rival, Playfish).
As a word of warning, do not assume that TrialPay or Offerpal will be free services. Many of the offers that give you microtransaction coinage cost something and give little in return. All of the offers require personal information, which might include your credit card or mobile phone numbe,r which then allows the company to charge you without you noticing. There are some legitimate, useful services bundled in amongst the potential scams, including Netflix, but as a whole one should be very cautious of any trial-based incentive. Scams abound in TrialPay and Offerpal, so your best bet is to not use them whatsoever.