Security through biology is an enticing idea. Since 2011, police departments across the U.S. have been scanning biometric data in the field using devices such as the Mobile Offender Recognition and Information System (MORIS), an iPhone attachment that checks fingerprints and iris scans. The fbi is currently building its Next Generation Identification database, which will contain fingerprints, palm prints, iris scans, voice data and photographs of faces. Before long, even your cell phone will be secured by information that resides in a distant biometric database.

Unfortunately, this shift to biometric-enabled security creates profound threats to commonly accepted notions of privacy and security. It makes possible privacy violations that would make the National Security Agency's data sweeps seem superficial by comparison.

Biometrics could turn existing surveillance systems into something categorically new—something more powerful and much more invasive. Consider the so-called Domain Awareness System, a network of 3,000 surveillance cameras in New York City. Currently if someone commits a crime, cops can go back and review sections of video. Equip the system with facial-recognition technology, however, and the people behind the controls can actively track you throughout your daily life. “A person who lives and works in lower Manhattan would be under constant surveillance,” says Jennifer Lynch, an attorney at the Electronic Frontier Foundation, a nonprofit group. Face-in-a-crowd detection is a formidable technical problem, but researchers working on projects such as the Department of Homeland Security's Biometric Optical Surveillance System (BOSS) are making rapid progress.

In addition, once your face, iris or DNA profile becomes a digital file, that file will be difficult to protect. As the recent nsa revelations have made clear, the boundary between commercial and government data is porous at best. Biometric identifiers could also be stolen. It's easy to replace a swiped credit card, but good luck changing the patterns on your iris.

These days gathering biometric data generally requires the cooperation (or coercion) of the subject: for your iris to get into a database, you have to let someone take a close-up photograph of your eyeball. That will not be the case for long. Department of Defense–funded researchers at Carnegie Mellon University are perfecting a camera that can take rapid-fire, database-quality iris scans of every person in a crowd from a distance of 10 meters.

New technologies will also make it possible to extract far more information from the biometrics we are already collecting. While most law-enforcement DNA databases contain only snippets of the genome, agencies can keep the physical DNA samples in perpetuity, raising the question of what future genetic-analysis tools will be able to discern. “Once you have somebody's DNA, you have all sorts of very personal info,” Lynch says. “There is a lot of fear that people are going to start testing samples to look for a link between genes and propensity for crime.”

Current law is not even remotely prepared to handle these developments. The legal status of most types of biometric data is unclear. No court has addressed whether law enforcement can collect biometric data without a person's knowledge, and case law says nothing about facial recognition.

It is unfortunate that the only body capable of enacting broad and lasting protections against the misuse of biometric data is the U.S. Congress. Yet perhaps legislators can agree that the law needs to catch up with technology. If so, they should start with principles that Lynch and the Electronic Frontier Foundation have proposed. Among other things, such legislation should limit the amount and type of data that the government can store and where they can be stored. It should restrict the collation of different types of biometric data into a single database. And it should certainly require that all biometric data be stored in the most secure manner possible.

Identity theft, fraud and terrorism are real problems. Used properly, biometrics could help protect against them. But the potential for misuse is glaringly obvious. We must begin setting rules to govern the use of these technologies now.