When accepting data back from a post-back, assume someone has tampered with it and re-validate it. In other words, never use an ID in a hidden field that you didn’t expect someone could change (they can change them). Do not use simple “Id” fields (person.Id, etc) to identify a person, if it’s not possible to the PersonActionIdentifier then use Guids. Even then, realize Guids are also not hidden or secret, and therefore must not be accepted without revalidating they haven’t been tampered with. This is especially true for public facing blocks.