WASHINGTON — The biggest challenge for the gang of hackers in Russia said to have amassed 1.2 billion sets of user names and passwords, wasn’t actually stealing them. It’s putting that data to use.

The pilfered records, associated with about 500 million unique e-mail addresses, were discovered by Hold Security, a Milwaukee-based company that sells information-security and risk-management services. The findings were based on seven months of research, though the company didn’t give a time period for the theft or name any websites that were hacked.

While Hold said it’s the largest known cache of stolen personal information, not all the records were current and the company couldn’t say if financial accounts were linked. Also, user names and passwords are less valuable than credit-card data and Social Security numbers, said Peter Toren, a partner in the Washington-based law firm Weisbrod, Matteis & Copley.

“People should step back and question what kind of accounts are we talking about,” Toren, who served as an attorney for the Department of Justice’s computer crime and intellectual property section from 1992 to 1999, said in a telephone interview. “Do I really care if they find out what kind of music I listen to?”

Serious criminals, often in Eastern Europe, steal payment-card numbers. The theft of at least 40 million such numbers from Target Corp. last year was one of their biggest hauls.

The bigger threat is that the Russian hackers could use whatever information they obtain to build profiles of people, which can be sold on the underground Internet market or used to obtain fake driver licenses or passports, Toren said.

“There are just so many ways information can be used to an individual’s disadvantage, even if the likelihood of such uses is speculative.” said Woody Hartzog, assistant professor at the Cumberland School of Law at Samford University in Birmingham, Alabama.