The Stealth Key (also called Anti-Boss Key) helps you hide the erasure process from other users or people around, with a keyboard shortcut. This will activate the Stealth Mode, that is, east-tec Eraser will start running in the background with pre-selected options (e.g. erase your Internet traces in stealth mode).
All you have to do is define a combination of keys to enable/disable the stealth mode. You may do this from the Dashboard Settings + Advanced Settings of each module -> Hotkeys page.
In case of emergency, just press the keyboard shortcut so that you can keep on using your PC peacefully without having to worry about the erasure process being exposed.