TechCrunch:
As the outcry by advertisers grows louder than the assurances from Google that click fraud is not a substantial problem, representatives from Google and Yahoo! publicly stated today that they would accept independent click fraud audits. Of course the true independence of any audit will need to be closely watched. The pay per click advertising business is a monster – with billions of dollars exchanged annually. Yahoo! has made more than $9 billion since 2004 from all of its online advertising, Google more than $13 billion since 2001.