This is an example of a very simple way to defeat inline, hardware-based keystroke loggers, like the kind that go inbetween your computer and the keyboard.

They work by storing anything you type (64,000 characters or more) in their internal memory for retrieval later.  They require no software to operate and are not detectable without a physical search of your computer.

Their simplicity is also their downfall.  The Key Katcher draws its power from the +5 VDC line on computer's internal keyboard port.  This is usually PIN 4 on the PS/2-style (mini-DIN) keyboard connector.  By disabling the keyboard's +5 VDC power line internally within the computer, anything connected to the keyboard port will not receive any power, including any Key Katchers (or any keyboards).

To power the keyboard you just need to run an external +5 VDC power line, or you can even use batteries within the keyboard.

Block Diagrams

Pictures

• Picture 1  PS/2-style mini-DIN keyboard connector - overview.  The yellow disk is a resettable fuse for both the mouse and keyboard +5 VDC power lines.
• Picture 2  PS/2-style mini-DIN keyboard connector - underside view.  You need to cut a trace on this particular motherboard as the fuse powers both the mouse and keyboard power lines.
• Picture 3  AT-style DIN keyboard connector - overview.  The fuse has been cut and lifted.  I cut the wrong side of the fuse, be sure to cut the side of the fuse going to the keyboard connector.  You'll want to utilize the fuse in your new power line.
• Picture 4  AT-style DIN keyboard connector - test setup.  You'll need to probe the power lines within the computer and the keyboard itself.  It appears every computer/keyboard combination will be different.

Notes

Think Geek Key Katcher

Key Katcher - With Installation Photos