Canada's tax collector has said that hackers exploiting the Heartbleed bug have stolen data about hundreds of citizens from its computers.

The Canada Revenue Agency said that the haul involved social insurance numbers as well as other as yet unidentified information.

The attack is the first confirmed exploit of the cryptography flaw to result in the loss of sensitive data.

The agency said it would send registered letters to those affected.

"Based on our analysis to date, Social Insurance Numbers (SIN) of approximately 900 taxpayers were removed from CRA systems by someone exploiting the Heartbleed vulnerability," the agency said on a message posted to its homepage.

"We are currently going through the painstaking process of analysing other fragments of data, some that may relate to businesses, that were also removed."