Two threat-intelligence firms warn the voter information for some 35 million U.S. citizens is being sold on a popular hacking forum.

Researchers for Anomali Labs and Intel471 said in a joint statement they believe the breach "represents the first reference on the criminal underground of actors selling or distributing lists of 2018 voter registration data," reported ZDNet.

The stolen data, according to the researchers, contains details such as full name, phone numbers, physical addresses, voting history and other voting-related information.

The peddled data comes from 19 states.

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ZDNet pointed out that some states consider the data public and allow it to be downloaded for free, but not all states have that policy.

The 19 states are Montana, Louisiana, Iowa, Utah, Oregon, South Carolina, Wisconsin, Kansas, Georgia, New Mexico, Minnesota, Wyoming, Kentucky, Idaho, Tennessee, South Dakota, Mississippi, West Virginia and Texas.

ZDNet said users commenting on the forum where the data is sold suggested it might come from the Robocent incident in June, in which thousands of U.S. voters' data was exposed by a robocall firm.

But the seller claims "data is refreshed each Monday of every week," suggesting either continued access to the compromised servers or another source.

"Certain states require the seller to personally travel to locations in-state to receive the updated voter information. This suggests the breach is not necessarily a technical compromise but rather an extensive operation involving cooperation within the election organizations," the Anomali Labs team said.