A security system in which more than one form of authentication is implemented to verify the legitimacy of a transaction. In contrast, single factor authentication (SFA) involves only a user ID and password.

In two-factor authentication, the user provides dual means of identification, one of which is typically a physical token, such as a card, and the other of which is typically something memorized, such as a security code.

Additional authentication methods that can be used in MFA include biometric verification; such as, fingerscanning, iris recognition, facial recognition, and voice ID. In addition to these methods, smart cards and other electronic devices can be used along with the traditional user ID and password.

A type of user authentication that uses voiceprints and pattern recognition software to verify a speaker.

An adaptation of biometrics, voice ID relies on the fact that vocal characteristics, like fingerprints and the patterns of people's irises, are unique for each individual.

The criteria that a voice ID system bases decisions on are created by the shape of the speaker's mouth and throat, rather than more variable conditions.

Because of the relative permanence of the characteristics it measures, the technology is not likely to be fooled by an attempt to disguise a voice, and is not generally affected by changes that can make a voice sound quite different to the human ear; such as, a bad cold or extreme emotion.

During enrollment for a voice authentication system, a user's voice is recorded, creating what is called a voiceprint for comparison with samples taken for user identification.

To foil attempts to fool the system with a prerecorded voice sample, people may be asked to read or repeat a list of words which they can then be requested to repeat in random combinations.

Voice ID systems have been used in a variety of security-related applications. The United States judicial system has used the technology, on a limited basis, for about ten years to ensure that prisoners incarcerated in their homes or out on temporary passes were where they were supposed to be.

Voice-based systems could potentially be used effectively in any situation where secure authentication is especially important. Banks and credit card companies are increasingly turning to voice authentication as a means of decreasing the potential for fraud and identity theft and, at the same time, cutting the costs associated with customer verification.

Voice authentication products are available from a number of vendors, including Vocent, Nuance Communications, Courion Corp., and VoiceVault.