Google Adsense Policies clearly states that “Clicks on Google ads must not result in a new browser 
window being launched.” Adsense publishers are neither allowed to alter the HTML code nor can they give their visitors an option to open Google ads in a new browser window.
But according to a report published in The New York Times, a majority of web users are responding to banner ads indirectly - they avoid clicking the actual banner advertisement on the website but type the advertiser’s URL directly in their browser.
The main reason for this behavior is that consumers want to continue staying on the website where they first saw the ad. Clicking the ad unit would mean navigating off the current webpage. An Adsense Policy That May Be Hurting Google’s Revenue » Digital Inspiration © Amit Agarwal