The Rochester public school system in the US state of Minnesota suffered a significant cyber attack that forced it to close all of its 42 schools on Monday.

On April 7, the school district said that it identified “irregular activity on its network” and had to temporarily take its systems offline to investigate and assess the security incident.

“Our technology staff have since been working non-stop with third-party experts to investigate and address this situation,” the district said in a statement.

In a YouTube video, District Superintendent Kent Pekel said that the District has decided to not hold any classes on Monday as with the lack of internet access it would be difficult to continue with regular classes. Sports and extracurricular activities would, however, continue as normal.

“I regret the impact that not having students report on Monday will have on our families, and I also regret needing to share this information during what for many of our families is a holiday weekend and at the tail end of spring break.

“I ask for your patience and understanding as we work to resolve this situation as quickly as possible,” Pekel said in the video.

In a separate update, the school district said that it will try to hold classes with “no or reduced access to technology systems starting on Tuesday, April 11.” At the time of writing, Rochester public school’s website, rochesterschools.org/ was still offline.

The school district is yet to comment on how threat actors infiltrated its network, if any data has been stolen, or whether the school has received a ransom demand.

This news comes within days after the Jefferson County School System in Alabama suffered a significant cyber attack that disrupted its phone lines and internet services. In February, Minneapolis Public School also announced that it suffered an “encryption event” that affected internal IT systems and disrupted several systems including its internet, phones, cameras, badge access, printers, building alarms, and more.

On March 7, the infamous Medusa ransomware group listed Minneapolis Public Schools as its latest victim on its data leak site. The group said it gave the school district until March 17 to pay a ransom of US$1 million in exchange for deleting all data or US$50,000 to extend the deadline by another day. The group also said that it was willing to sell all stolen data to anyone willing to pay a million dollars.

Once the deadline expired, the ransomware group published the data stolen from MPS. Ian Coldwater, a cybersecurity expert and an MPS parent, said the leaked data included current and former student records, parent contacts, home addresses, IDs with pictures, grades, sensitive disciplinary and health records, budgets, contracts, grant information, building layouts, payroll and human resources information, and more.