Parts of the Canada Revenue Agency website were also shut down over the same vulnerability, smack in the middle of tax season.
The Statistics Canada website was hacked by an unknown attacker, officials said in a briefing in Ottawa on Monday, leading to the site being taken offline from Thursday until Sunday.
Parts of the Canada Revenue Agency (CRA) website, including a tax filing portal, were also shut down for two days smack in the middle of tax season due to the site containing the same "internet vulnerability" as Statistics Canada's site, officials said, although the CRA website was not hacked.
The vulnerability was in Struts2, a release of an Apache web server project. Officials could not say how long the affected software was used by the government, but the vulnerability was fixed on Sunday.
"These types of vulnerability reports are issued daily," said Scott Jones, Deputy Chief of IT Security in Canada's Communications Security Establishment, the country's NSA analogue, during a call with media outlets including Motherboard. "Some hackers on the internet were actively attempting to exploit this vulnerability."
No other government sites use the affected software, Jones added, but others may be affected. "Anyone using this technology in the private or public sector should immediately install the patches," he said.
"The unpatched version of the software […] had the potential to be exploited," Jennifer Dawson, Deputy Chief Information Officer for the Treasury Board of Canada Secretariat, also said during the call with journalists.
According to Gabrielle Beaudoin, director of communications at Statistics Canada, no personal information was taken by the hacker.
"We have data tables, publications [on that server]," Beaudoin said, adding that no personal or sensitive information was available. "It's all information that's already in the public domain, but there was an intrusion on that server."
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