Why would they? What's your recourse as a consumer if they fuck up your hardware? In the extremely unlikely event you manage to get it in front of a Court, they could point to the 3 other ad networks also present on the same page, and to the wider internet just infested with the fucking things. Odds are incredibly long you could even prove you were infected with whichever virus, and then what do you get? A few years of identity theft protection, a new phone if you're VERY lucky?