To designers of secure computer systems, identity is a core concept of authentication. Identity theft is said to occur when one person gains control of credentials (such as credit card numbers or passwords) which belong to another, thus becoming able to masquerade as the "stolen" identity.

Identity might rely on:

• Name
• Address
• Credit card number ¹
• Postcode or ZIP Code
• Phone number
• National Insurance number (UK) or Social Security number (US)¹
• DNA ²
• Iris in the eye ³
• Fingerprints ⁴
• Birthmarks
• Dental records ⁵
• Tattoos ⁶

1. This is individual only to you, unless an administrative mistake is made, or someone gets hold of this number by reading it from paper in your trash.
2. This is individual to you, your identical twin, your clone, or anyone who can obtain a sample of your DNA and amplify it
3. This is individual only to you, or anyone wearing a suitable contact lens with the pattern of your iris on, or the 1% of the population who will be recognised as you as a false positive.
4. This is individual only to you, unless someone copies your fingerprint off any clean surface using a digital camera and then prints it out and transfers it to a relief pattern on a piece of gel.
5. This is individual only to you. Be prepared to have a dental X-ray every time you need to identify yourself.
6. This could be individual only to you: watch out. See ka-tzetnik.

Note: all of the other identifiers listed are unlikely to be unique to you, and allow confusion between yourself and the previous or subsequent occupants of your address and users of your phone number.

See also Recognition of human individuals, identity (social science) and change.