The Canada Revenue Agency (CRA) says it now knows what caused the problems that led it to shut down its computer system for income tax filing. The government agency says it has traced the source of the problem to software maintenance conducted on March 4.

The CRA is experiencing electronic system difficulties that prevent the public from accessing some electronic services for personal returns such as NETFILE, TELEFILE and EFILE.

It has have temporarily shut down public access to electronic services to ensure the integrity of taxpayer information.

The CRA says it has a team working to restore its systems to normal operations, but it will be a matter of days before the system problems are completely resolved. The team is currently working to bring all systems back online gradually.

The security and integrity of taxpayer data has not been compromised. This problem is not the result of illegal activity, computer hackers or a virus.