There are known concerns about HTTP Referrers. For example, each time you click a link in the list of search results, the browser will send along its request to the Web site, the referrer site you have been coming from. It has interesting consequences. Imagine you have type in your favorite search engine
This keywords will appear in the resulting referrer. You can disable the HTTP Referer so that the browser is not sending it with your HTTP requests. In Opera, go to opera:config#UserPrefs|EnableReferrer, then uncheck the box, and finally save.