Would you like to protect your computer when you leave it unattended? You can use Predator!
All you need to do is use a USB stick: when inserted it will be possible to use the computer normally, but when it is removed the computer is automatically locked! No one will be able to access it, even if they know the access password!
For a user guide: fribby.net/predator/?lang=en
Official page: No longer exists.
Free Download Predator for Windows (version 2.4 is free for personal use, from version 3 it is instead necessary to purchase a license to use the program):
File
License terms
(iii)PREDATOR Free Edition application may be copied and redistributed freely.