Also, just a follow up: many organizations in my industry are actually completely blocking most major ad networks (including AppNexus and DoubleClick) at their

Also, just a follow up: many organizations in my industry are actually completely blocking most major ad networks (including AppNexus and DoubleClick) at their proxies due to all the issues caused by malvertising. My organization is currently looking into it. Malvertising is a much more serious problem than people think, though I think this article and whitepaper is slightly FUD.