The Quebec branch of the hacking collective Anonymous claimed responsibility for the incident in a series of posts on Twitter.
The group says it also infiltrated the website of the police brotherhood union. That site was back online Saturday morning.
In a series of tweets Anonymous denounced the actions of police during a recent series of anti-austerity demonstrations against the government of Premier Philippe Couillard. The heated demonstrations have led to clashes between protesters and police.
The group is calling for the dismissal of a police officer photographed while using pepper spray against the protesters.
Anonymous hinted at further action on Saturday in a tweet that claimed they could control most of the city's networks.
A police spokesman confirmed Saturday the site was breached. He said no personal information was at risk.
The site went back online shortly after 1 p.m. Sunday.
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