School districts that were affected by a PowerSchool data hack in December are now facing extortion attempts by cyber criminals, according to the K-12 ed-tech company.

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.

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.