Carleton University is warning students and employees after an external group apparently attempted to hack the school's IT network.
The school warned that any system accessible from the main network that is Windows-based may have been compromised.
The school's IT security unit is attempting to secure the network from further attacks.
"To reduce traffic on the network, it is recommended that users refrain from using Microsoft Windows systems at the current time and shut down your computer," the school warned in a message posted on its website and its Facebook page.
Ransomware messages demand bitcoin payments
The school said people may see ransomware messages appear on their screens, demanding payments in bitcoins.
"Users are asked to ignore all messages seeking a payment and are encouraged to report these messages to the CCS Help Desk at ext. 3700 or email@example.com," the school said in a statement.
David Kenyi, a volunteer at the International Students Service Office, said he got a push notification on his phone of the system shutdown.
"It's really brought a lot of problems," said Kenyi. "Normally when people come here they register for events. Now they [are doing] it manually, using pen and paper, and later I will need to put that into the system."
"It's been really hard, I can't access my email. There are things I need to do, as well as my colleagues," he added. "We are kind of stuck."
The university remains open and classes are continuing. Officials said they would be providing another update Wednesday morning.