Known as malvertising - a portmanteau of "malicious" and "advertising" - the attack saw hackers hijack advertising platforms to deliver fake browser updates for the three most popular Windows browsers.
Because advertising inventory can appear on high-profile websites, criminals are increasingly attempting to hijack these platforms to inject malware into a large number of victims' computers.
The sophisticated filtering that ad networks offer to vendors can also be used by cyber criminals to target users running specific software containing vulnerabilities that can be exploited.
The attack affecting PornHub and its advertising network was committed by a group known as KovCoreG, said Proofpoint, which attempted to infect browsers with the Kovter ad fraud malware.
Advertising fraud is so prevalent on the internet that some advertisers only receive $0.01 for every $1 of impressions they pay for, according to independent ad fraud expert Dr Augustine Fou.
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