As any web publisher will tell you advertising income has gone through the floor for this very reason. By rights a lot more of the web should be behind paywalls but nobody is willing to be the first to break ranks.Because the advertising is often, without telling you (or even telling the owners of the sites on which it appears) doing more than just showing you pictures of products and services to enhance your lifestyle - I don't really trust any online adverts not to carry malware.