Canada's government on Friday ordered all federal department websites vulnerable to the "Heartbleed" bug to be shut down.
"The chief information officer for the government of Canada issued a directive to all federal government departments to immediately disable public websites that are running unpatched OpenSSL software," Treasury Board President Tony Clement said a statement.
"This action is being taken as a precautionary measure until the appropriate security patches are in place and tested."
It is unclear how many government websites are affected, or how long they may be down.
The move comes two days after Canada's tax agency shuttered its website, ahead of an April 30 annual income tax filing deadline.
The recently-discovered flaw in online-data scrambling software OpenSSL allows hackers to eavesdrop on online communications, steal data, impersonate websites and unlock encrypted data.
OpenSSL is commonly used to protect passwords, credit card numbers and other data sent via the Internet.
More than half of websites use the software, but not all versions have the same vulnerability, according to heartbleed.com.
Cyber security firm Fox-It estimates that the vulnerability has existed for about two years, since the version of OpenSSL at issue was released.
Computer security specialists, website masters and others began fretting about the "Heartbleed" bug this week after several reports of hacking.
Explore further: Heartbleed bug causes major security headache (Update 3)