In any case, I haven't seen anyone here mention the ad networks themselves. Every once and a while we would get a complaint about a bad ad - it wouldn't dismiss, etc. Over time, we whittled down our network list to ad networks that strictly test and vet the ads they serve, no matter how much time that takes.
The networks blaming a "rogue advertiser" means they're not even passing ads on their network through automated malware detection software, and so they have responsibility here.
Creepiness factor aside, the explosion of networks is a problem, because so very few are actually providing more than a basic service. We really should be holding networks responsible for their ads.
We did, and we haven't had a complaint for a very long time.
Edit: this doesn't absolve Forbes, especially if they did nothing to correct the problem.
Edit 2: by "we should hold the networks responsible" I mean "we the publishers" - and as that "we" we still have a responsibility to our users/consumers. See Edit 1.