On one of my servers on this is login prompt:
I've surprisingly found one more user in the list (not available on this sample picture from the internet) with name "\". I don't see such a user in /home folder. I don't remember myself adding this user to the system. What might this be? What can I do to remove it?
I don't know how he got there but to remove him you just need to become root and then run this command:
Note that the username might not be John Smith, instead try to get his username using this command to view the file that contains the passwords:
The username will be on the left.