Canada Revenue Agency says it has temporarily shut down parts of its website due to Internet security concerns over a bug known as "Heartbleed," preventing Canadians from filing their tax returns.

In an emailed statement, the CRA said the partial shutdown is a preventative measure to protect private information that could fall into the wrong hands.

Restoration of public access to EFILE, NETFILE and other services will likely resume over the weekend, the CRA said in a release issued Wednesday afternoon.

“After learning late yesterday afternoon about the Internet security vulnerability named the Heartbleed bug that is affecting systems around the world, the CRA acted quickly, as a preventative measure, to temporarily shut down public access to our online services to safeguard the information we hold,” the release reads.

Earlier Wednesday, Revenue Minister Kerry-Lynne Findlay indicated it could be some time before the system was back up and running.

"We're investigating, we're working on it," Findlay told reporters in Ottawa.

The CRA said it recognizes the shutdown is posing a "significant inconvenience" for taxpayers at a crucial time of year, and indicated it will give consideration to those who are unable to file on time.

The “Heartbleed” security flaw has exposed millions of passwords, credit card numbers and other sensitive data to potential theft by computer hackers who may have been secretly exploiting the problem before its discovery, the Associated Press reported Wednesday.

The bug affects the encryption technology that is supposed to protect online accounts for emails, instant messaging and a wide range of electronic commerce. The breach went undetected for two years.

Experts are telling people to change all their online passwords.

Many learned of the CRA service interruption when they were prevented from filing taxes or logging into a personal account on the agency's website. The notice informs visitors the shutdown is security related.

“To protect the security of taxpayer information, we have temporarily shut down public access to our electronic services,” the website says. “We are working to restore these services as soon as possible in a manner that ensures they are safe and secure.”

This is a busy time of year for the tax agency, as people file returns electronically and track the progress of refunds online. The deadline for filing a 2013 tax return is April 30.

As of the end of March, the agency had received 6.7 million returns, with 84 per cent filed electronically.

- With files from The Canadian Press and The Associated Press.

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