In the 1997 film Gattaca, DNA police could identify a person using just a fleck of discarded skin or a single hair.

This was a huge boon for catching bad guys, but it also meant that no one's genetic information was private.

Last week, the Translational Genomics Research Institute in Phoenix said that a team of scientists led by David Craig had developed a method for identifying an individual using only a smidgen of their DNA, even if it is mixed with hundreds of other people's DNA.

The breakthrough will greatly improve police forensics that uses DNA from crime scenes to hunt down lawbreakers and will help identify victims of disasters such as plane crashes and terrorist bombings with greater accuracy.

It also can be used to search for individual genetic signatures in the huge public databases at the National Institutes of Health and elsewhere. These repositories store thousands of people's DNA—which is supposed to stay anonymous—that were used in studies looking for genes that influence or cause disease.

The N.I.H., the Wellcome Trust Case Control Consortium in Britain, and the Broad Institute at the Massachusetts Institute of Technology were among the organizations that responded to the study's release by shutting down public access to DNA repositories.

This comes just a few months after Congress passed the Genetic Information Nondiscrimination Act to protect individuals from insurance companies and employers who would use their DNA against them.

The new law, however, is slim on protections from searches and potential abuses by law enforcement and the government, gaps that need to be addressed immediately by the new Congress in light of these new technologies.

Translational Genomics, often referred to as TGen, revealed its new method in a study published on August 29 in the open-sources journal, PLoS Genetics, published by the Public Library of Science.

"It is now possible to know with near certainty that a particular individual was at a particular location, even with only trace amounts of DNA and even if dozens or even hundreds of others were there too," Craig, the paper's senior author, said in a press release issued by the institute.

The breakthrough comes because of new "gene array" technologies from companies such as Illumina and Affymetrix that can quickly test for up to a million genetic markers, as opposed to current police forensics labs that test for only about 20 markers. That is often not enough markers to make a positive match.