This sounds very conspiracy-theory-ish to me. The more likely explanation is that some ad network allowed malware ads to go through which triggered the block.
If that's your definition of a sketchy ad network then there aren't many that aren't sketchy. Google serves ads that do that all the time. It only took me a few seconds to find this misleading fake download link ad being served by Google on one of the download pages of download.com: http://i.imgur.com/wYAfr7z.png
Would Google blacklist download.com for serving malicious google ads? Somehow I doubt it.
eh, maybe it does.
Not defeding anyone, ad business is highly volatile, especially in grey areas of the web.