To prevent this from happening, many people use a large number of proxy servers for the purpose of clicking. These are basically trojans, located on computers throughout the world (though mostly in the US). What's even more daunting is that these clicks will appear to originate from an actual computer so such scams are really hard to detect.
And don't think this happens only in isolated instances. There is a great deal of illegal activity in this domain.
In fact there's so much that if search engine companies don't increase their security with such programs as AdSense, such criminal behavior could become more become even more damaging.
Google has a very strict policy regarding click fraud, and it has sued those employing such techniques in the past. But while the search engine giant tries its best to minimize the risk of click fraud there's certainly room for a lot of improvement.
It is estimated that more then 20% of the clicks that follow an AdSense link are just done in order to get money from the person paying for the ad. Some people believe the number of fraudulent clicks to be even twice as large.
There are a great deal more schemes involving click fraud, such as groups of AdSense publishers clicking each other's links (which is referred to as "clicking rings", or spamming people so that they click such links.
Despite Google still holding click fraud on a leash, the phenomenon is certainly raising concerns for the advertisers on AdWords, but despite this advertising with Google's AdSense still remains more profitable for the advertiser, as opposed to traditional untargeted advertising schemes.
There are some means of protection against such schemes and all advertisers should be savvy enough to employ them. Many advertisers choose to avoid the content network all together for fear of click fraud.
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