Canada's tax agency says it expects to have its online systems up and running again over the weekend.
The Canada Revenue Agency says it's still working on a fix to a major international security concern that forced the shutdown of its electronic filing services.
In the meantime, the agency says it is investigating whether the private information of Canadians was compromised.
The tax agency temporarily cut off public access to its electronic services today, saying the action was taken as a precaution.
The shutdown came after the Canadian Cyber Incident Response Centre issued a warning to system administrators about a coding flaw known as Heartbleed.
Other federal systems are also being assessed for their vulnerability to the threat, although it's not clear whether more online services will be taken down.
The affected services at CRA include EFILE, NETFILE, My Account, My Business Account and Represent a Client.
But the problem is international in scope, forcing banks, websites and social media sites to assess their vulnerability.
Heartbleed was only revealed this week, but computer experts say it's been in computer systems for the past two years.
It is a busy time of year for the tax agency, as people file returns electronically in time for the April 30th deadline.
As of the end of March, the Canada Revenue Agency had received 6.7 million returns, with 84 per cent filed electronically.