On the campaign settings page, find the Blocked sites and ad exchanges section and enter the site domains, mobile app IDs, or names of ad exchanges that you want to block from serving your ads (combined maximum of 1000).
On the Statistics page in the “By site” report, choose sites in the list and block them in the Action list.
If you add a site to the blocked list, campaign ads won't be served on either content pages of this site or search results for it. If you block impressions for an ad exchange, campaign ads won't be served on any of the sites in that ad exchange. However, if a site from a blocked ad exchange is in the YAN or another ad exchange and you do block that site individually, then ads will continue to be served on tht site. You cannot opt out of your ads being served on Yandex search and Mail.ru
You can see what sites your ads were served on in the Report wizard by using the Ad platform name cross section.
Excluding sites and ad networks may negatively affect the performance of your ad campaign and cause you to lose some of your potential audience.