A 60-day study conducted by the Association of National Advertisers and ad fraud detection company White Ops came to a conclusion likely to unsettle many digital ad buyers: purchasing ads from premium publishers does not protect marketers from fraud.

"Advertisers who assume that traffic to premium publishers is free of bots risk losing large amounts to intentional or unintentional bot fraud," the report stated.

The finding -- perhaps the most startling in the study, which revealed advertisers will waste $6.3 billion dollars on ad fraud in 2015 -- demonstrates that ad fraud is not limited to the bare bones websites which are often exposed in fraud operations.

"The reputation of the publisher is no longer a reliable benchmark to predict bot traffic level," the report stated.

In one case study detailed in the report, a well-known lifestyle publisher served 98% of an advertiser's video ads to bots. "Out of almost 4,000 total video impressions from the placement, fewer than 100 were served to humans," the report stated.

The bot traffic premium publishers are serving stems primarily from traffic they've purchased from third-party sources, said White Ops Chief Scientist Dan Kaminsky. "The strongest predictor of bots was whether the traffic was sourced," he said. On average, the study found bots accounted for 52% of purchased traffic.

Mr. Kaminsky stopped short of saying publishers buying traffic are directly contributing to the fraud problem. "What I can tell you is that when they source traffic, they may know it, they may not know it, but more often than not, the people coming to their site are not people," he said.

One-quarter of the fraud detected by White Ops showed up on Alexa's 1,000 most visited websites, according to Mr. Kaminsky.

Ad injection, which is when browser extensions insert ads into publisher websites without the publisher's knowledge or approval, also contributed to the fraud on premium websites, according to the study.

The advertising industry is intent on holding publishers buying fraudulent traffic accountable for their actions. Speaking to Ad Age after the announcement of an anti-fraud initiative set up by the Interactive Advertising Bureau, the American Association of Advertising Agencies and the Association of National Advertisers, IAB exec-VP Mike Zaneis said: "Too many people are engaging in acts of omission, where you sort of turn a blind eye, and it's sort of, 'Well this is common practice, everybody buys traffic from this source, so I'm just doing what everybody else is doing.' That's not going to be okay anymore."

A few other key findings from the report:

• 11% of all display ads were served to bots
• 17% of programmatic display ads were served to bots
• 67% of bot traffic stemmed from residential IP addresses
• Bot traffic spiked between midnight and 6 a.m. and on weekends

The ANA's study spanned 181 campaigns run by 36 advertisers. More than 5.5 billion impressions on 3 million domains were monitored.