Malvertising is the means to an end for an attacker and the ends haven t changed much. Hackers use the tactic to build botnets, distribute banking malware, or even deliver complicated exploits used in targeted attacks. Malvertising campaigns are generally found out for a matter of hours and are burned to the ground before an ad network can take action against a phony account. Security company Invincea says the money to jack up the bidding is usually stolen or generated from click-fraud and other malware campaigns.
Source: https://threatpost.com/ad-networks-ripe-for-abuse-via-malvertising/111840/