Personally Identifiable Information (PII), as used in information security, is information that can be used to uniquely identify, contact, or locate a single person or can be used with other sources to uniquely identify a single individual. The abbreviation PII is widely accepted, but the phrase it abbreviates has four common variants based on personal, personally, identifiable, and identifying. Not all are equivalent, and for legal purposes the effective definitions vary depending on the jurisdiction and the purposes for which the term is being used.
Although the concept of PII is old, it has become much more important as information technology and the Internet have made it easier to collect PII, leading to a profitable market in collecting and reselling PII. PII can also be exploited by criminals to stalk or steal the identity of a person, or to plan a person's murder or robbery, among other crimes. As a response to these threats, many website privacy policies specifically address the collection of PII, and lawmakers have enacted a series of legislation to limit the distribution and accessibility of PII.
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The following data, often used for the express purpose of distinguishing individual identity, clearly class as PII under the definition used by the U.S. Office of Management and Budget (described in detail below):
The following are less often used to distinguish individual identity, because they are traits shared by many people. However, they are potentially PII, because they may be combined with other personal information to identify an individual.
When a person wishes to remain anonymous, descriptions of them will often employ several of the above, such as "a 34-year-old white male who works at Target". Note that information can still be private, in the sense that a person may not wish for it to become publicly known, without being personally identifiable. Moreover, sometimes multiple pieces of information, none sufficient by itself to uniquely identify an individual, may uniquely identify a person when combined; this is one reason that multiple pieces of evidence are usually presented at criminal trials. It has been shown that, in 1990, 87% of the population of the United States could be uniquely identified by gender, ZIP code, and full date of birth.[1]
The U.S. government used the term "personally identifiable" in 2007 in a memorandum from the Executive Office of the President, Office of Management and Budget (OMB),[2] and that usage now appears in US standards such as the NIST Guide to Protecting the Confidentiality of Personally Identifiable Information (SP 800-122).[3] The OMB memorandum defines PII as follows:
A term similar to PII, "personal data" is defined in EU directive 95/46/EC, for the purposes of the directive:[4]
Another term similar to PII, "personal information" is defined in a section of the California data breach notification law, SB1386:[5]
The concept of information combination given in the SB1386 definition is key to correctly distinguishing PII, as defined by OMB, from "personal information", as defined by SB1386. Information, such as a name, that lacks context cannot be said to be SB1386 "personal information", but it must be said to be PII as defined by OMB. For example, the name John Smith has no meaning in the current context and is therefore not SB1386 "personal information", but it is PII. A Social Security Number (SSN) without a name or some other associated identity or context information is not SB1386 "personal information", but it is PII. For example, the SSN 078-05-1120 by itself is PII, but it is not SB1386 "personal information". However the combination of a valid name with the correct SSN is SB1386 "personal information".[6]
The combination of a name with a context may also be considered PII; for example, if a persons' name is on a list of patients for an HIV clinic. However, it is not necessary for the name to be combined with a context in order for it to be PII. The reason for this distinction is that bits of information such as names, although they may not be sufficient by themselves to make an identification, may later be combined with other information to identify persons and expose them to harm.
According to the OMB, it is not always the case that PII is "sensitive", and context may be taken into account in deciding whether certain PII is or is not sensitive.[7]
Recently lawmakers have paid a great deal of attention to protecting a person's PII. One of the primary focuses of the Health Insurance Portability and Accountability Act (HIPAA), is to protect a patient's PII. The U.S. Senate proposed the Privacy Act of 2005, which attempted to strictly limit the display, purchase, or sale of PII without the person's consent. Similarly, the (proposed) Anti-Phishing Act of 2005 attempted to prevent the acquiring of PII through phishing.
U.S. lawmakers have paid special attention to the social security number because it can be easily used to commit identity theft. The (proposed) Social Security Number Protection Act of 2005 and (proposed) Identity Theft Prevention Act of 2005 each sought to limit the distribution of an individual's social security number.
On the other hand, many businesses see this increasing load of legislation as excessive, an unnecessary expense, and a barrier to progress. The increasing complexity of the laws might force companies to consult a lawyer just to engage in simple business practices such as server logging, user registration, and credit checks. Some have predicted such measures may inhibit the industry as a whole, lowering wages and creating a barrier to entry. For this reason, a number of privacy laws stress the "acceptable uses" of PII, such as Massachusetts' Public Records Law and Fair Information Practices Act.
State Laws and Significant Court Rulings
Proposed Federal Bills
Federal Law
Further examples can be found on the EU privacy website[10]
In forensics, the tracking down of the identity of a criminal, personally identifiable information is critical in zeroing in on the subject. Criminals will go to great trouble to avoid leaving any PII; they wear masks (faces and hair are PII), gloves (fingerprints are PII), clothing that covers personal marks (tattoos and scars are PII) and avoid writing anything in their own handwriting (handwriting can be PII). Also, more modern 'masks' may be used, such as using a proxy IP address to avoid being tracked online as easily.
In some professions, it is dangerous for a person's identity to become known, because this information might be exploited violently by their enemies; for example, their enemies might hunt them down or kidnap loved ones to force them to cooperate. For this reason, the United States Department of Defense (DoD) has strict policies controlling release of PII of DoD personnel.[11] Many intelligence agencies have similar policies, sometimes to the point where employees do not disclose to their friends that they work for the agency.
Similar identity protection concerns exist for witness protection programs, women's shelters, and victims of domestic violence and other threats.