The general website for government services, canada.ca, as well as the site of Canada's spy agency, the Canadian Security Intelligence Service, were among those affected.
Tony Clement, the cabinet minister responsible for the Treasury Board, confirmed on his Twitter account that government websites had been cyber attacked.
Shared Services Canada, the agency responsible for the government's information technology infrastructure, did not respond immediately to a request for comment.In a video posted on YouTube, the informal online activist group known as Anonymous said it was responsible for the attack. The video said the anti-terrorism law, recently passed by the Canadian Senate, violated human rights and targeted people who disagree with the government.