The Quebec branch of the hacking collective Anonymous claimed responsibility for the hack 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.
Anonymous hinted at further action in a tweet that claimed they could control most of the city's networks.
A spokesman for the Montreal police confirmed the site was hacked. He said no personal information was at risk. The site is used mostly as an information portal for citizens.
Also on HuffPost