The school's administration, professors and students had been without access to emails for 10 days, before technicians were able to "isolate the effects of the attack" and use a key to unlock its server.
To obtain the key, the university said it "paid a ransom totalling about CanUSD20,000 that was demanded as part of this 'ransomware' attack."
"There is no indication that any personal or other university data was released to the public," it said.
Such attacks typically involve an unknown person or group infiltrating and encrypting a computer or a network, rendering the data inaccessible until a ransom is paid in exchange for a key or decryption method.
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University executive Linda Dalgetty defended the decision to pay, telling reporters: "We do world-class research here... and we did not want to be in a position that we had exhausted the option to get people's potential life work back."
"Extraordinarily upset that UCalgary paid a ransom," Shipley said in a Twitter message. "They have unnecessarily placed other Canadian schools in danger.