(Bloomberg) -- Canada’s largest school district is investigating a cyber incident, adding to a series of ransomware attacks that have caused disruptions to companies and public institutions in the country.

The Toronto District School Board alerted parents Wednesday in an emailed letter, noting that the attack happened when an unauthorized party gained access to the board’s technology testing environment. The TDSB said its cybersecurity team took immediate steps to preserve data and safeguard critical operations, adding that its systems are operational and haven’t been impacted. Toronto police have been notified.

The TDSB said it’s investigating to determine impacts of the incident and whether any personal information may have been affected. The board serves approximately 238,000 students in nearly 600 schools throughout Toronto.

The incident follows a February cyberattack on the City of Hamilton that disabled some information technology systems. The Toronto Public Library, Canada’s biggest library network, suffered a ransomware attack in October that took months to recover from. Companies have also been targeted, including an April attack on western Canadian retailer London Drugs Ltd. that forced the company to shut dozens of stores for a week.

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