Contextual advertising is regardeded as one of the most efficient Internet-marketing tools.

But even considering the fact that it has passed many stages during which the mechanisms of adaptation to the needs of buyers and advertisers were improved, there still remain too many "loopholes" for all sorts of frauds nowadays.

Click fraud, also known as invalid clicking, is one of such loopholes. This term defines the activitiy of multiple transitions to the advertised page("clicks"), which leads to inefficient waste of budget. However, experienced webmasters are able to detect this kind of activity, and are eager to share their skills. Let’s consider the main factors that help identify click-fraud:

1. An abrupt increase in the number of advertising links’ clicks. It's natural for early days because people see the ads of products they need for the first time and go through the links. But if contextual advertising operates some time with regular transitions and there is a sudden leap in transiction graph – it may be a bad signal and you should analyze web-statistics.
2.  Another factor indicating click-fraud is unnatural decrease in the number of orders (or other desired activities - the amount of subscribers, the number of comments and requests for consultation etc.).
   
3. Too fast waste of budget. If ad-budget is spent unusually quickly especially during advertising low demanded products (specialized equipment that is rarely purchased etc.) the SEO should thoroughly analyze any mass transition to such ad-links and various behaviour factors.
   

Any contextual-ads network offers advertisers different tools to research th efficiency of their ad-campaigns. The most comprehensive is the indicator of CTR - click through rate or CTR rate.

It shows the ratio of clicks on advertisements to the total number of display. High demanded goods and well-written advertisements usually have higher click through rate. However, in most cases the index is not very high - from 5% to 15% and barely reaches 20%.

In the case there is an abrupt leaps or steady growth without proportional increase in the number of required transactions (purchases and other actions described above) on the transition graph SEO-specialist should suspend the ad-campaign and reconfigure it’s setting. If it is found that a large number of transitions is made from one ip-address you can disable this address in the settings (ad it to the black-list).

Also you have topay attention to CTR on partner sites. According to official statistics of the main contextual networks they offer lower CTR than those in search engines. However, this is true only if the partner sites are additional to advertising in search results but not the only chosen option of placing.

These are the main and sufficient means of click-fraud protection.