TORONTO — A class-action lawsuit has been filed on behalf of Canadians affected by the massive Capital One data breach that was disclosed on July 30.

The suit, launched by lawyers at Ontario firm Diamond & Diamond, seeks compensation for Canadians who applied for credit cards from Capital One between 2005 and 2019.

“This data breach could have very serious ramifications for those affected with regards to their future finances,” said Jeremy Diamond, managing partner at the firm, in a statement.

The suit’s representative plaintiff is Rina Del Guidice of Bolton, Ont., who obtained a Costco Wholesale MasterCard through Capital One.

It notes that Capital One also operated credit cards offered by other merchants including the Hudson’s Bay Co.

Darryl Singer, the firm’s lead lawyer on the suit, said in a statement that the stolen information could pose a risk to identity theft for years.

“What makes this breach so egregious is that it includes identifying information such as someone’s name and social insurance number that cannot be changed.”

The statement of claim seeks that the lawsuit be certified as a class action calling for more than $350 million in financial compensation and other forms of relief for the plaintiffs.

Capital One has said that as many as six million people in Canada may have been affected by the breach, and that one million social insurance numbers were among the leaked sensitive information. The breach also exposed the data of roughly 100 million U.S. clients, including about 140,000 Social Security numbers and 80,000 linked bank account numbers.

The company said it would start to inform Canadians affected by the breach this week either by letter or email, but not by phone.

The Office of the Privacy Commissioner of Canada said last week that it had launched an investigation into the data breach.

The Diamond & Diamond suit has been filed with Ontario Superior Court in Toronto. Vancouver-based Charney Lawyers said last week that it planned to file a similar class action against Capital One.