Pornography website operators that have been using Google's ad network to lure new traffic have been shown the door. The search giant recently enforced a new policy that bans the promotion of hardcore pornography from its ad network.

Google first revealed intentions to update its advertising policy back in March. At that time, the search giant said AdWords policies on adult sexual services, family status and underage or non-consensual sex acts would be updated in late June 2014 to reflect a new policy on sexually explicit content.

In a recent e-mail sent to an AdWords Advertiser that was picked up by VentureBeat, Google said they'll no longer accept ads that promote graphic depictions of sexual acts including, but not limited to, hardcore pornography; graphic sexual acts including sex acts such as masturbation; genital, anal, and oral sexual activity.

The decision is already having an impact on porn site operators. Theo Sapoutzis, chairman and CEO of AVN Media Network, told CNBC that he was caught by surprise by the change. Sapoutzis said he was one of the first advertisers to sign up for AdWords back in 2002.

"It's something that's been [untouched] for 12 years, so you don't expect change is going to start happening," he said.

For those unfamiliar, AdWords is Google's advertising platform for those looking to place ads on Google's sites and other properties around the net. While Google may have a solid footing in search and mobile, it's their advertising network that is responsible for the vast majority of their earnings.

During the most recent quarter, for example, Google earned $13.8 billion in ad revenue. This accounted for around 90 percent of the company's overall revenue during the three-month period.