Cybercriminals demanded ransom payments from school districts nationwide this week, using millions of K-12 students’ sensitive data as leverage after the files were stolen from education technology giant PowerSchool in a massive cyberattack late last year.

Public school employees around the state received threatening emails asking for money in exchange for deleting the information.

PowerSchool is warning that the hacker behind its December cyberattack is now individually extorting schools, threatening to release the previously stolen student and teacher data if a ransom is not paid.