Are Social Security numbers always 9 digits?

Today we take the 9-digit composition of the SSN as a given, but in 1935 and 1936 many other schemes were considered. In early November 1935, the Social Security Board adopted an identifier composed of 3 alphabetic characters representing geographic areas and 5 numeric characters.

Is it safe to give last four digits of SSN?

Although it’s important to always be safe and smart about who you’re giving your SSN to, the last four numbers of the SSN are the most important to protect. For this reason, it is recommended not to share it with anyone, not to include it in emails, and not to use it as your security PIN.