Malicious hackers are now using ad networks to deliver malware to unsuspecting users. Advertisers turn to these services to deliver their messages across multiple — sometimes thousands of — websites. Ad networks have caught on and have started checking suspicious ads to show the correct, unadulterated websites. Hackers have also begun buying legitimate space on ad networks. Make sure every external link comes from a site known to use good security practices or at least require external security audits or send the external party a security checklist to which they must respond.”]
Source: https://www.csoonline.com/article/2612267/don-t-fall-prey-to-ad-networks-peddling-dicey-links.html