Mountain View, CA — Search giant Google (NASDAQ: GOOGL) has enforced a block on advertisements that promote “sexually explicit content” from its advertising network – Google Adwords. Thus, Google will no longer allow ads that contain sexual imagery. Google’s AdWords ads appear on millions of sites across the Web. It appears to be the first time that the policy on explicit content is being changed.

What’s surprising is ads for dating sites, and adult entertainment are still allowed. The new rules will be in effect, beginning this week. Google has however cleared that the ad ban will not affect search results, but only the advertisements that visitors find displayed at the top of the page.

The new changes were already being communicated via email to advertisers. Here is a message from it, as follows:

Beginning in the coming weeks, we’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.

When we make this change, Google will disapprove all ads and sites that are identified as being in violation of our revised policy. Our system identified your account as potentially affected by this policy change. We ask that you make any necessary changes to your ads and sites to comply so that your campaigns can continue to run.

In addition to banning sexual imagery, AdWords advertisers are forbidden from marketing prostitution services, erotic massages and “intimate companionship services. The change in guard from Google is indicative of the steps it wants to improve users’ experiences with AdWords.