From clickfraud.com

In March 2004, Michael Andrew Bradley allegedly attempted to blackmail Google for $100,000, threatening to unleash across the web software that he built to facilitate click fraud - but last month, the case against Bradley was suddenly dropped.
No one is sure why the prosecution dropped the case, but it may be because Google didn't want it to go to court, writes ABC News. Fiercely secretive about the methods it uses to curb click fraud, Google might have feared that if the case went to trial, those methods would have come up for examination - becoming a matter of public record.

"I think that the one plausible explanation is that Google did not want any information about its technology to get out into the public," said Brian Kabateck, a class action attorney who represented thousands of small businesses in a lawsuit against both Google and Yahoo.

Google spokesman Barry Schnitt admitted that concern about revealing company secrets played a role in the decision, but also suggested that Bradley was no longer a threat.

An estimated average of 14.6 percent of the clicks advertisers are billed for are fraudulent, according to Outsell Inc., an information industry research group. Outsell estimates that click fraud is a $1.3 billion problem: $800 million wasted on fraudulent clicks plus $500 million no longer spent on pay-per-click online advertising.