LONDON -- You can ditch your computer and leave your cellphone at home, but you can't escape your DNA.

It belongs uniquely to you - and, increasingly, to the authorities.

Countries around the world are collecting genetic material from millions of citizens in the name of fighting crime and terrorism - and, according to critics, heading into uncharted ethical terrain.

Leaders include the United States - where the Supreme Court recently backed the collection of DNA swabs from suspects on arrest - and Britain, where police held samples of almost 7 million people, more than 10 percent of the population, until a court-ordered about-face saw the incineration of a chunk of the database.The expanding trove of DNA in official hands has alarmed privacy campaigners, and some scientists. Recent leaks about U.S. surveillance programs by former NSA systems analyst Edward Snowden have made people realize their online information and electronic communications may not be as secure as they thought. Could the same be true of the information we hold within our genes? DNA samples that can help solve robberies and murders could also, in theory, be used to track down our relatives, scan us for susceptibility to disease, or monitor our movements.

Earlier this year Yaniv Erlich, who runs a lab at MIT's Whitehead Institute for Biomedical Research, published a paper in the journal Science describing how he was able to identify individuals, and their families, from anonymous DNA data in a research project. All it took was a computer algorithm, a genetic genealogy website and searches of publicly available Internet records.

"It was a very weird feeling - a 'wow' feeling," Erlich told The Associated Press. "I had to take a walk outside just to think about this process."

Erlich says DNA databases have enormous positive power, both for fighting crime and in scientific research. But, he said, "our work shows there are privacy limitations."

Few would disagree about the power of DNA to catch criminals - and to clear the innocent. Hundreds of wrongly convicted people around the world have been freed thanks to DNA tests. A recent AP investigation found that at least 24 men in the United States convicted of or charged with murder or rape based on bite marks on the flesh of victims have been exonerated since 2000, thanks to DNA evidence.

Ethical qualms have done little to stop the growth of genetic databases around the world.

The international police agency Interpol listed 54 nations with national police DNA databases in 2009, including Australia, Canada, France, Germany and China. Brazil and India have since announced plans to join the club, and the United Arab Emirates intends to build the world's first database of an entire national population.

The biggest database is in the United States - the FBI's Combined DNA Index System, or CODIS, which holds information on more than 11 million people suspected of or convicted of crimes.

It is set to grow following a May Supreme Court ruling that upheld the right of police forces to take DNA swabs without a warrant from people who are arrested, not just those who are convicted. (Policies on DNA collection vary by state; more than half of the states and the federal government currently take DNA swabs after arrests.)

The court's justices were divided about implications for individuals' rights. Justice Anthony Kennedy, for the five-judge majority, called the taking of DNA a legitimate and reasonable police booking procedure akin to fingerprinting.