What policies and procedures are in place to prevent someone with a nefarious intent from changing my status to "deceased" and access my private information?
Welcome to the "Community.FamilySearch" Forum.
I am just another 'lowly' User/Patron ...
As far as I was aware ...
[ And, ONLY referencing the 'lowly' Users/Patrons, NOT the "Administration" of 'FamilySearch' ... ]
[ and, IF, you are a Member of the Church; THEN, NOT, the 'Church', in relation to your Membership Record ]
NO Other User/Patron, can access YOUR ("Personal") 'FamilySearch' Account.
That Said ...
NO Other User/Patron, can access YOUR ("Personal") 'FamilySearch' Account, to "Change", your actual 'Status', from "Living", to "Deceased".
Here are some "Knowledge Articles" in 'FamilySearch':
All That Said ...
Another User/Patron CAN enter/create "You"; as, an individual/person, in "Family Tree", of 'FamilySearch', with the 'Status' of "Deceased".
It can happen ...
And, apart from (as you indicate), "... with a nefarious intent ..."
We ALL make MISTAKES ...
NONE of us are PERFECT ...
IF, you find yourself (or, you find another person, that you know), to be "Living", in "Family Tree", of 'FamilySearch'; as, "Deceased"; THEN, it is a SIMPLE matter, of "Changing" the 'Status' of "Death", from "Deceased", to "Living", add a "Reason Statement" (ie. "Reason This Information Is Correct:"); and, "Save".
Although, the 'Status' DOES NOT "Change" IMMEDIATELY ...
Your "Edit" (ie. in fact a "Request"), go DIRECTLY to 'FamilySearch' "Support".
'FamilySearch' "Support" will investigate; and, provided they agree, with you; which, I am certainly the will (in just about every case; except, if you are referencing another individual/person, other than yourself), 'FamilySearch' "Support" CHANGES the 'Status', from "Deceased", to "Living"; and, you DO NOT 'see' that "Version" of yourself; as, it then goes into the "Private Spaces" of the User/patron who "Created" it. This may take a day or two (unless, there is a significant 'Backlog'.
Of course, you could just contact (ie. "Message") the Other User/Patron who created that "Version" of you, let them know that you are actually "Living"; and, request that they "Change" the 'Status', from "Deceased", to "Living". This DOES in MANY cases, actually work (generally, with humble apologies); but, may take time.
The former action, of you yourself, "Changing" the 'Status', from "Deceased", to "Living", is often much faster; and, you know, it WILL get actioned.
Here is a "knowledge Article", 'FamilySearch':
I hope that this all helps/assists, somewhat.
Though it may be true that no one can access Matthews personal account and access his private information.
that doesn't prevent someone else from entering a Family Tree Record for Matthew and marking that record as deceased. (which is what I assume Matthew was alluding to)
BUT Brett is totally right - doing such - - does NOT in any way give them (or anyone) access to your private info under your private account - which is still linked to a LIVING person record in your private space (and not the same record that someone else may have created and even marked as deceased under the same name)