Millions of school children have their personal data exposed in hackers' leak sites, with a tally from Emsisoft ransomware analyst Brett Callow showing that data from over 1,200 K-12 schools across the U.S. have been published by ransomware groups so far this year, reports NBC News.

K12 Security Information Exchange Director Doug Levin noted that public school systems have even more inadequate data protections, compared with many private businesses.

"I think it's pretty clear right now they're not paying enough attention to how to ensure that data is secure, and I think everyone is at wits' end about what to do when it's exposed. And I don't think people have a good handle on how large that exposure is," Levin said.

The vulnerability of school systems to hacks should prompt parents to freeze their children's credit while they are underage to prevent identity theft or fraud, said Identity Theft Resource Center President Eva Velasquez.

"We should for all intents and purposes believe that for the most part, all of our data's been compromised," said Velasquez.