The Do Not Track feature lets users notify websites, via an HTTP request, that you are not willing want to be tracked or receive targeted advertising. To enable this feature under the Opera web browser, proceed as explained below:
Under Opera 15
Click on the Opera button > Settings > Privacy.
In the "Privacy" section, checked "Send a `Do Not Track' request with your browsing traffic".
For the previous versions of Opera
Click on the Opera button > Settings > Preferences
Go to the Advanced tab > Security.
In the right pane, check "Ask websites not to track me".