[TUHS] Questions about * and ! in the password field of passwd and shadow

[Ron Natalie via TUHS]

Back when the (encrypted) passwords were in /etc/password, a * was a 
common way to make accounts that could not be logged into.   This goes 
back forwever (putting a blank password field in just meant there was no 
password required to log in).   This predated /etc/shaddow and even the 
inclusion of the “salt” characters at the beginning of the passwords.   
The ! to disable wasn’t something I saw.   It must have come later (but 
before people started using programs to manipulate these things).