You might as well assume your entire SSN is public. Most of them have been leaked someplace or other, and for anyone who was an adult before about 2000 it was c

You might as well assume your entire SSN is public. Most of them have been leaked someplace or other, and for anyone who was an adult before about 2000 it was common to have them pre-printed on your personal checks. It's only in the past few decades that they have suddenly become "secret." That someone who called you on the phone happens to know your SSN last four or even the entire number should not confer any trust on your part.