PGP Freeware, the encryption and decryption utiltiy, includes "PGPscreen" which can be launched as an application, from the PGP menu, by pressing command-option-L or automatically after certain period of inactivity. It is a screen locker like "Lockout" except it is free. It is immune to debuggers. When the screen is locked it has the PGP logo floating around. It is not for MacOS X. It requires a private key (which would be the same key you would use to encrypt stuff with) because it has the password in it (or passphrase as they call it). A key can be created with PGPkeys (also included). http://www.pgpi.org/products/pgp/versions/freeware/mac/7.0.3/