In recent years, many entities in the private, public, and government sectors have reported the loss or theft of sensitive personal information. These breaches have raised concerns in part because they can result in identity theft--either account fraud (such as misuse of credit card numbers) or unauthorized creation of new accounts (such as opening a credit card in someone else's name). Many states have enacted laws requiring entities that experience breaches to notify affected individuals, and Congress is considering legislation that would establish a national breach notification requirement. GAO was asked to examine (1) the incidence and circumstances of breaches of sensitive personal information; (2) the extent to which such breaches have resulted in identity theft; and (3) the potential benefits, costs, and challenges associated with breach notification requirements. To address these objectives, GAO reviewed available reports on data breaches, analyzed 24 large data breaches, and gathered information from federal and state government agencies, researchers, consumer advocates, and others.