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.

Software maker said it paid its attackers even as the true size of the theft is still unknown.

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.