Click fraud is a big business, and so is detecting it. Click-fraud auditing firm Click Forensics has raised a $10 million B round, led by Sierra Ventures. Also participating is Austin Ventures and Shasta Ventures, who invested in the company’s $5 million A round last January.

Advertisers and Website can subscribe to the company’s service, which claims to be able to identify fraudulent clicks on ads, and even clicks from competitors. Of course, if Google were to ever defeat click fraud, Click Forensics would be out of business. But what is the chance of that happening?