While technically there is no legal issue with respect to having a leap year birthday, people born on February 29th (often called “leapers”) may face some problems, particularly with regard to medical or government records. Some computer systems do not accept February 29th as a valid date, or alternatively do not take into account leap years and print invalid expiration dates (such as February 29, 2015, which did not exist) on their driver’s licenses, insurance policies, and other documents. Because of the potential social issues related to having a birthday that is only officially recognized every four years, instances have been recorded of physicians altering birth certificates so that the birth date would not fall on February 29th — a practice that is illegal.