Click fraud is expected to reach $1.1B for 2005. By 2008, this is estimated to grow $1.68 B, an increase of over 45%,
In 2004, at least $500 million in pay- per-click online advertising expenditure was wasted through click fraud.
The estimated cost of click fraud to online advertisers will be in excess of $1.6 billion
As much as 70% of annual online advertising spending is wasted because of click fraud
Corrupt affiliates of ad networks such as Google and Yahoo account for 85% of all click fraud.
The above data is taken from http://www.clickfraud.com/.
Click fraud occurs in pay per click online advertising when a person, automated script or computer program imitates a legitimate user of a web browser clicking on an ad, for the purpose of generating an improper charge per click.