They weren't designed to be used as general-purpose identifiers by non-government entities, either, but here we are.

My college classes used to post grades, on paper, taped to the wall, listed by SSN.

Which, assuming it was in the last 50 years or so (assuming it didn't have individual non-compulsory signed and dated written consent of every individual whose grades were so posted) a violation of federal law (specifically, the Family Educational Rights and Privacy Act of 1974.)