Editors notes: Upon further investigation people who are not your friends on facebook can not be banned from seeing your profile and commenting, however you can set your profile on private and that will prevent them from trolling you.
They’re on your friends list and can’t be blocked, who are they?
If you search under Settings>Blocked and search the term “facebook security,” a slew of user accounts that are unblockable will appear.
However, if you’ve been getting trolled and find an unblockable account it is because they’re not on your friends list, not because they belong to facebook security. You can search any term, not just “facebook security” to find un-blockable accounts.
Who are they? When investigated some accounts have the term Facebook security in their profile description. Could mean nothing at all.