There are few issues in search marketing more thorny and convoluted than click fraud. It's the elusive problem, the industry scourge that seems to defy definition. Everyone wants to know the extent of click fraud, but to date, there seems to be no credible numbers to attach to the problem. A recent BusinessWeek 'Investigation' called it the 'dark underground' of the Internet, a dizzying collection of scams and deceptions that inflate advertising bills for thousands of companies of all sizes. The BusinessWeek article pegged the occurrence of click fraud at 10% to 15% of ad clicks representing roughly $1 billion in annual billings. Unfortunately, the reporter used some questionable sources and math to come up with this number.