Facebook is preparing advertisers for the “clear history” tool that will let people erase their personal data from the social network, affecting ad targeting.

On Tuesday, Facebook announced the long-awaited “clear history” feature would roll out in the coming months. It will allow users to delete data that the social network gathers from websites and apps outside of Facebook, and no longer use that data for advertising.

Some of Facebook’s most popular marketing technology like the Facebook Pixel and Custom Audiences could be rendered useless if a person erases their tracks. Brands use the pixel, computer code, to tag a user when he or she visits their websites—and then hit them with an ad when they are back on Facebook. If people clear their pixel, they won’t be accessible that way again, unless they visit the website again and rebuild their history.