OTTAWA (Reuters) - Right in the heart of tax-filing season, the Canada Revenue Agency (CRA) shut down access to online tax services on Wednesday because of an Internet bug that has made data on many of the world's major websites vulnerable to theft by hackers. "We have received information concerning an Internet security vulnerability named the Heartbleed Bug," the CRA, the government's tax collector, said. It added that the shutdown was a preventive measure. Experts say the Heartbleed bug, found in widely used Web encryption technology, is one of the most serious security flaws uncovered in recent years. The tax filing deadline in Canada is April 30, 15 days later than in the United States, but the CRA said it would give consideration to taxpayers unable to comply with their filing requirements because of the service interruption. "The CRA recognizes that this problem may represent a significant inconvenience for individual Canadians, representatives and businesses that count on the CRA for online information and services," it said. "Please be assured that we are fully engaged in resolving this matter and restoring online services as soon as possible in a manner that ensures the private information of Canadians remains safe and secure." (Reporting by Randall Palmer; Editing by Peter Galloway)