A computer bug called "Heartbleed" is causing major security headaches across the Internet due to its breakdown of a widely used encryption technology that is supposed to protect online accounts for a variety of online communications and electronic commerce, according to CNET.com.

The breakdown was revealed earlier this week and now websites are trying to fix the problem, CNET.com reported.

Security researchers who uncovered the threat are particularly worried about the lapse because it went undetected for more than two years, according to CNET.com.

The computer hackers have either been secretly exploiting the problem before its discovery or it is also possible that no one took advantage of the flaw before its existence was announced late Monday, CNET.com reported.

In Canada, the Revenue Agency shut off public access to its website "to safeguard the integrity of the information we hold," according to a Wednesday notice posted on its website, CNET.com reported. The agency hopes to re-open its website this weekend.

The United States Internal Revenue Service said in a statement Wednesday that it's not affected by the security hole, CNET.com reported.

"The IRS advises taxpayers to continue filing their tax returns as they normally would in advance of the April 15 deadline," the agency said.

Computer security experts are advising people to consider changing all their online passwords but Google assured its users they were protected against the Heartbleed bug before any damage could be done and that no Google account passwords need to be modified, according to CNET.com.

Facebook also said its online social network had purged the Heartbleed threat, but encouraged "people to take this opportunity to follow good practices and set up a unique password for your Facebook account that you don't use on other sites," CNET.com reported.

At Yahoo, the repairs have been made on a list of services that includes its home page, search engine, email, finance and sport sections, Flickr photo-sharing service and its Tumblr blogging service, according to CNET.com.

Yahoo is advising its users to "rotate their passwords" and add a backup mobile number to the account, CNET.com reported.