One of the most pernicious activities that Facebook does is to track you when you’re not on their website, and even if you’re not logged into Facebook or don’t have a Facebook account. They often do this using cookies that websites deliver to your browser. Facebook has recently provided a way to view and edit “off-Facebook activity,” which the company defines as “activity that businesses and organizations share with us about your interactions, such as visiting their apps or websites.”
The word “apps” above is important. Facebook gets data not just from websites you visit, but also from apps you use, and you have no way to turn that feature off. Facebook then uses this data to serve you ads based on your activity. You can use content blockers or tracker blockers in your web browser to prevent this tracking, but they have no effect on apps.
You can “disconnect” this activity, but this won’t change the number of ads you see; ads will just not be “personalized” as before.
Read the rest of the article on The Mac Security Blog.