"Pay-per-click," by far the most popular form of online advertising, recently came under fire as charges of rampant "click fraud" gather steam on the Web.Google and Yahoo! earn the majority of their money through sales of advertising to tens-of-thousands of online merchants, companies, and professional.In fact, some estimate that 99% of all Google's revenue comes from advertising sales. Unfortunately, allegations of click fraud may well rain on Google's otherwise sunny parade and cause a whole s.