Thanks for replying, Emilly.
I think that I found the reason:
I have the ESET anti-virus, and while activating the Anti-Theft system, it creates a Phantom Account (and sending mails every time using it).
I deactivated the system and the user deleted.
Simple reason... but I didn't know that this system creates this.
(And I don't want anyone to use my computer with no password).
Is there and way using this system with no account added?
Again, thank you very much.
Ishai.