HUNTSVILLE, Ala. (AP) — One of Alabama’s largest public education systems is closed because of what officials called a computer cyberattack involving ransomware, and it was unclear Wednesday when classes will resume.

The Huntsville City Schools system — with almost 23,000 students, more than 2,000 employees and about 40 schools — closed early on Monday because of the problem and will remain shut down at least through Friday, officials said. Officials said classes would resume “as quickly as possible,” but it was unknown when that might be.

Police are investigating the attack, and system spokesman Craig Williams urged students and staff members Wednesday not to use any school-issued computers or other devices.

“When it comes to devices, turn them off and keep them off,” said Williams. It's unclear what data might have been compromised.

A statement from the system said administrators and teachers were being brought back into schools in stages, but computers can't be turned on, so virtual lessons that have become common during the coronavirus pandemic aren’t an option. Teachers who can’t use computers are making paper lessons for the system’s students. Workers began distributing curbside meals for lunch on Wednesday.

The shutdown caused fresh problems for students and parents who have already spent weeks dealing with the fallout from the coronavirus pandemic.

“My first thought was, well, that’s extremely 2020,” Benjamin Shapiro, who has one child in sixth grade and another in seventh grade, told WAAY-TV.

Torie Serkez, a mother of three, was concerned about how the shutdown would affect her children, particularly a first-grader who is autistic.

“Even from the Thanksgiving break, my son has suffered,” Serkez said. “My son suffers if he’s out of school for more than a day.”

In a typical ransomware attack, hackers gain access to a computer system and threaten to withhold or destroy information unless money is paid. School officials haven't released details on the type of attack that forced the shutdown, but former prosecutor Jay Town told WAFF-TV that regaining data can be tricky.

“You are to some degree trusting that the criminals themselves are going to release the network back to you in exchange for some form of payment,” said Town, a former U.S. attorney now with Gray Analytics. “Again that’s only if some payment is necessary because you are unable to recover the network, restore the network, break the encryption.”

In Maryland, the 115,000-student Baltimore County school system was forced to close the day before Thanksgiving because of a ransomware attack. Officials said virtual lessons were resuming on Wednesday.