The estimates for digital ad fraud vary widely, depending on who published it, what was measured, when it was measured, the assumptions that went in, and the technologies used for detection.

1. January 2015 / Page 0marketing.scienceconsulting group, inc.
Dr. Augustine Fou
Estimates of the Rate of Ad Fraud Vary Widely
DSPs/Networks Security Vendors
3%
Dstillery, Oct 9, 2014_
“findings from two independent third parties,
Integral Ad Science and White Ops”
3.7%
Rocket Fuel, Sep 22, 2014
“Forensiq results confirmed that ... only 3.72% of
impressions categorized as high risk.”
57%
Telemetry, May 26, 2014
“Telemetry found that 57 per cent were “viewed” by automated
computer programs rather than real people.”
25 - 50%
WhiteOps, Jul 14, 2014
“digital ad fraud outbreak – one that gobbles up roughly $14 billion in
advertising spend and between 25 and 50% of ad spend per campaign”
45%
Solve Media, Sep 19, 2014
“suspicious web activity dropped to 45% – still a high figure, but an
improvement nonetheless from the high of 61% in Q4 2013”
low high
“Whatever the number, there is no refuting that there is
ad fraud... and job one is to find the fraud impacting
your business and extinguish it....” -- Dr. Augustine Fou