A Kid calls the Help Desk to Complain a computer problem: Kid: When I Type Computer Password

A kid calls the help desk to
Complain a computer problem:

Kid: when i type computer password,
It just shows star star star star.
What is the joke?

Help desk: dear kid, those stars are to
Protect you, so that if a person standing behind,
He can't read your password.

Kid: yeah, but stars appear even when there
Is no one standing behind me.