Bell Canada says an anonymous hacker has obtained some customers' names and telephone numbers as well as e-mail addresses.
The telecommunications giant says illegally accessed information included approximately 1.9 million active e-mail addresses and approximately 1,700 customer names and active phone numbers.
Bell says there is no indication that any financial, password or other sensitive personal information was accessed.
The company says the incident is not connected to the recent "WannaCry" cyberattack – which affected tens of thousands of companies, organizations and individuals in about 150 countries when it initially struck on Friday.
Bell says it took immediate steps to secure affected systems and has been working closely with the RCMP cyber crime unit in its investigation of the hack.
The company also says it is contacting affected customers.