Screenlock
This programm was accuracy created and tested, but I'm not responsible for any damage caused by using this progam.
Screenlock will stay in front of all programs and your desktop until you enter the correct password.
My standard password is "123".
Your password is saved as a SHA-512 hash value (As far as I know, SHA-12 is unbreakable (until now)).
Screenlock is automatically closed after you've entered the correct password.