Millions of people may have had their privacy compromised on a downtown San Antonio street in September. Data tapes that hold health information for about 4.9 million people who received treatment or had their tests processed at military facilities in Texas were stolen from a car belonging to an employee of a government contractor.

That theft is one of more than 370 major medical-information breaches posted on the U.S. Department of Health and Human Services (HHS) Web site since 2009, spotlighting the potential problems presented by electronic records that are intended to improve the health care system by making more information available at a faster speed. The breaches involve health information stored on computer networks and devices that include laptops and memory cards, as well as paper and X-ray records.