Police forces across the globe are expanding their collection of DNA. More than 54 countries have national police databases filled with millions of DNA samples.
In Britain, police can collect samples from anyone over 10 years old for even minor offenses, and they can keep it forever.
But the biggest database is in the United States. The FBI's Combined DNA Index System, or CODIS, contains information on more than 11 million people suspected of or convicted of crimes.
That database is about to grow much bigger after the U.S. Supreme Court in May upheld the right of police forces to take DNA swabs without a warrant from anyone who is arrested, not just those who are convicted.
The growing stockpile of DNA is cause for concern among privacy advocates and scientists.
"If it's not regulated and the police can do whatever they want ... they can use your DNA to infer things about your health, your ancestry, whether your kids are your kids," MIT researcher Yaniv Erlich said.
Earlier this year Erlich described how he was able to identify individuals and their families using anonymous DNA, a simple algorythm, genealogy charts, and records available on the Internet.
Alec Jeffreys, the British geneticist who discovered DNA fingerprinting in 1984, has warned that "mission creep" could see authorities using DNA to accumulate information on people's racial origins, medical history, and psychological profile.
Chris Asplen, who heads the Global Alliance for Rapid DNA Testing, argues that DNA is similar to the fingerprints and Social Security numbers that authorities already hold about millions of people.
Nevertheless, he said he does see the possibility for abuse.
"There is an argument to be made that because that biological sample exists, the government could go back and do other things with it that are not authorized by the law," he said. "It's a constant tension between government and people, particularly when technology is applied."