Two of Canada's largest banks on Monday reported "fraudsters" claimed to have accessed customer information.
Canadian Imperial Bank of Commerce and Bank of Montreal both issued statements saying they were informing customers potentially impacted by attacks.
The bank accounts of some 40,000 customers might have been breached, Simplii Financial, CIBC's online bank, said in a statement.
Separately, Bank of Montreal said in a statement it had been contacted by fraudsters claiming to have some personal and financial information for "a limited number" of clients.
Bank of Montreal Canada's fourth-largest bank, said it believed the attack came from outside the country, and that it took immediate steps to contain the damage.
CIBC said there's "no indication" that clients who use its main bank were impacted by the breach.