For police officers around the country, the genetic profiles that 20 million people have uploaded to consumer DNA sites represent a tantalizing resource that could be used to solve cases both new and cold. But for years, the vast majority of the data have been off-limits to investigators. The two largest sites, Ancestry.com and 23andMe, have long pledged to keep their users’ genetic information private, and a smaller one, GEDmatch, severely restricted police access to its records this year.

Last week, however, a Florida detective announced at a police convention that he had obtained a warrant to penetrate GEDmatch and search its full database of nearly 1 million users. Legal experts said that this appeared to be the first time a judge had approved such a warrant, and the development could have profound implications for genetic privacy.

“That’s a huge game-changer,” said Erin Murphy, a law professor at New York University. “The company made a decision to keep law enforcement out, and that’s been overridden by a court. It’s a signal that no genetic information can be safe.”