Hardware keylogger

Hardware Keyloggers can be used for keystroke logging. They plug in between a computer keyboard and a computer and log all keyboard activity on an internal memory. They are typically designed to have an innocuous appearance that blends in with the rest of the hardware. For example, Keyghost markets one that is "injection moulded to look exactly like an EMC Balun"[1], and most competing keyloggers (e.g. KeyDevil, KeeLoggers, KeyKatcher, Amecisco, etc.) have a similar design.

They are designed to work with PS/2 keyboards, and more recently with USB keyboards.

Hardware keyloggers have an advantage over software keyloggers as they begin logging from the moment a computer is turned on (and are therefore able to collect a BIOS password for instance), and do not require software installation (unlike software solutions).


[edit] How do they work?
All hardware keyloggers have to have the following:

A microcontroller - this interprets the datastream between the keyboard and computer, processes it, and passes it to the non-volatile memory
A non-volatile memory device, such as Flash - this stores the recorded data, even when power is lost
On the whole the recorded data is retrieved by typing a special password into a computer text editor. As the hardware keylogger is plugged in-between the keyboard and computer, it detects the password has been typed and then starts presenting the computer with "typed" data to produce a menu. Beyond text menu some keyloggers offer a high-speed download to speed up retrieval of stored data, this can be via USB mass-storage enumeration or with a USB or serial download adapter