The federal tax agency says its online services are up and running again after it blocked public access five days ago due to the so-called Heartbleed bug.
The Canada Revenue Agency says the security risk has been addressed, but added it will not apply interest or penalties to individual taxpayers filing their 2013 tax returns after April 30 for a period equal to the length of the service interruption.
Revenue Minister Kerry-Lynne Findlay says that means 2013 tax returns filed by May 5 will not incur interest or penalties.
The CRA has apologized to Canadians for the delay and inconvenience, but added it was necessary to ensure the agency's online services were safe and secure.
The Heartbleed bug is caused by a flaw in OpenSSL software, which is commonly used on the Internet to provide security and privacy.
The bug is affecting many global IT systems in both private and public sector organizations and has the potential to expose private data.