Hotlink protection is an optional feature to the Uploadcare CDN that allows you to protect your bandwidth by disallowing other domains from linking to the content (images/videos/other files) you have on the CDN. It allows you to restrict HTTP referrers in order to prevent others from embedding your assets on other websites. If you want to activate the feature you need to contact support and let us know about all of the domains that should have access to the resources hosted in Uploadcare storage.
Note that this feature works with custom CDN domains only.