The words "United Islamic Cyber Force" were sprawled in red letters in English across the top of a black page and there was also a link on the website to the group's Facebook page.
Several other sites that were hosted by the same server as the Bloc's were also targeted, including the website for a campsite.
But the Albanian-based group said it was targeting the separatist party.
In an email exchange with The Canadian Press, a spokesman wrote the cyber attack was carried out "simply because they lacked respect towards women who wear the hijab."
The group maintained that everyone has the right to wear whatever they want.
Asked why the Bloc Quebecois and no other federal parties were victims of the attack, the spokesman said the group wanted "to expel politicians and others on the Internet who detested Islam."
The Bloc recently indicated that it was opposed to the decision of a federal court judge to allow a veil to be worn during the Canadian citizenship swearing-in ceremony.
While the hacker group refers to the hijab, which covers the head, the judge actually ruled in favour of the niqab, which hides the face.
Bloc Quebecois spokesman Simon Charbonneau said no personal data was compromised during the hack.
"We're taking all the necessary precautions (and) we have complained to the police," he said.
The hacker's Twitter and Facebook accounts had been taken down Monday.