The limitation of most biometric technologies is that they require the purchase of an additional piece of hardware. In addition to the cost of these devices, the setup restricts a person's ability to use any computer that doesn't have the required piece of biometric hardware installed.

To get around this problem, BioPassword Inc. in Issaquah, Wash., takes a software approach to biometrics using keystroke dynamics -- an analysis of how long a person holds down each key and how long it takes to move from one key to another.

This method is derived from military applications. As recently as World War II, the military used Morse code for communications. Since Morse was a well-known public standard, the problem was how to verify who was actually sending the message.

"Using a methodology called 'the fist of the sender,' military intelligence identified that an individual had a unique way of keying in a message's dots and dashes, creating a rhythm that could help distinguish ally from enemy," says Greg Wood, BioPassword's chief technology officer.

Later, organizations started looking into applying this methodology to computer security. In the early 1980s, the U.S. National Bureau of Standards funded research by the Stanford Research Institute (now SRI International) into this area. SRI concluded that analyzing the keystroke dynamics used when entering a user ID and password was 98 percent accurate, and an initial patent was issued in 1989.