Hackers shut down the Canadian intelligence agency's website Tuesday, officials said.
The intrusion came two weeks after several Canadian government websites were disrupted by the hacker collective Anonymous in protest of a new anti-terror law that critics say tramples civil rights.
The suspect or suspects in this new case mused on Twitter about whether to "let CSIS back online and hit another government website", or continue attacking the Canadian Security Intelligence Service website with what appeared to be a denial of service attack flooding a network with useless traffic.
"How is a government/police supposed to protect you, if they can't even protect themselves," said another Twitter post, adding that the next target was the Royal Canadian Mounted Police website.
Jean-Christophe de Le Rue, spokesman for Public Safety Minister Steven Blaney, said the hack on the CSIS website is "another reminder of the serious security challenges and threats that we are facing."
"Security officials have confirmed that no personal information was compromised in this attack," he added.
Broadcaster CTV, citing anonymous sources, said the suspect is connected to Anonymous and had previously targeted several Canadian police websites in order to bring attention to the controversial Bill C-51.
The bill was enacted in response to the first terror attacks on Canadian soil last October, when a gunman killed a ceremonial guard and stormed parliament, and a soldier was run over in rural Quebec.
However, it has been widely decried as overreaching and an unprecedented assault on civil rights.
It criminalizes the promotion of terrorism, makes it easier for police to arrest and detain individuals without charge, and expands the Canadian Security Intelligence Service's mandate from intelligence collection to actively thwarting terror plots and spying outside Canada.