Recent quotes:

NoTrove Malware is Killing Ad Network - - Performance Marketing Insider

They are then displayed on unsuspecting websites through a variety of methods. This might include poor website management or using hacked credentials to take over a website. More effective is the breaking into established advertising networks and using them to place ads on thousands of small business websites and blogs. In February RiskIQ reported that advertising networks from Google, AOL and Rubicon were among those hacked into. This allows malvertising from the like of NoTrove to be placed on large numbers of websites including those of very large companies.