Tax department says online tax filing fix is a 'major' one

The Canada Revenue Agency says it now knows what caused the problems that led it to shut down its computer system for income tax filing, but warns it will still be days before it's fixed.

"Today is better than yesterday," CRA commissioner Michel Dorais told CBC News Wednesday. "We worked throughout the night and I'm pleased to say today that we've diagnosed the problem exactly."

Dorais said the problem began shortly after 20 maintenance operations were carried out on the weekend. On Monday, the tax department noticed "some irregularities" in its databases and quickly shut down all online access to Efile, Netfile and My Account. Dorais called it an infrastructure problem and said the data is completely secure.