St. Paul city officials say they hope to get systems back online by the end of the week, after what they’re calling a ransomware attack. They said they have not paid the ransom.

Mayor Melvin Carter says the city is going through “Operation Secure St. Paul,” which includes manually resetting the passwords of 3,500 city employees.

To explain what a ransomware attack is, professor Faisal Kaleem joined Minnesota Now with Nina Moini. He’s the director of cybersecurity and cyber operations programs at Metro State University.