This is a pretty important case. I'm surprised I'm not seeing more about it. I spoke with the FTC about targeting affiliate networks, so it's especially interesting to me for that reason as well.

Here's the meat:
"But didn’t LeadClick surely know of the fake new sites (it did)? And didn’t it “aid and abet” their use by providing affiliates with a “link” to the seller’s website (it did)? And shouldn’t all that be enough to make it liable under Section 5? No, LeadClick says, for the simple but dispositive reason that “aiding and abetting” is not a basis of liability under Section 5."
Another defense LeadClick makes, which is pretty silly is that they are an Interactive Service Provider.

Full article:
Does the FTC Have Legal Authority Over Affiliate Networks? | Law Offices of William I. Rothbard