Google product manager Shuman Ghosemajumder says a recent blog post misinterprets the rate of click fraud Google sees.

On Monday, blogger Andy Beal, having spoken with Ghosemajumder at a recent conference, concluded that Google's click fraud rate was less than 2%.

In a reply on his own blog, Ghosemajumder attempted to clarify what he said. "I never said that our click fraud rate is less than 2%," he wrote. "Instead, what I said is that the quantity of invalid clicks which we detect as a result of reactive investigations is a 'negligible proportion' of the total number of invalid clicks. Andy asked me if that percentage is less than 2%. I told him that I was not able to provide a bound [sic], but yes, 'negligible' certainly means less than 2% of invalid clicks."

"Invalid clicks" encompass both fraudulent clicks and others that Google chooses to discard. "There are a significant number of clicks that we mark as invalid which we know have nothing to do with fraud," Ghosemajumder explained in a phone interview. "When we do that, we reduce our own revenues in order to benefit our advertisers. We do so because we'll benefit in the long run by providing them with the best ROI."

The total number of invalid clicks Google detects, according to Ghosemajumder, is a single-digit percentage.

Nearly all of these invalid clicks, he says—98% plus—are detected proactively, meaning Google catches them before the advertiser is billed.

The remaining fraction, less than 2% of the invalid click total, gets detected reactively following an investigation initiated because of an advertiser's complaint that prompts Google to refund some portion of the cost of the clicks called into question.

All of which is to say that Ghosemajumder believes click fraud is an issue Google has well in hand.

Click auditing companies claim the total number of invalid clicks is closer to 14%. Google has suggested that click auditing companies have an interest in exaggerating click fraud to justify their services.

As for the number of undetected invalid clicks, that number, by definition, remains unknown.