A Can$760 million (US$578 million) class action lawsuit has been launched against the owner of affair-seeking website Ashley Madison on behalf of Canadian users whose personal information was hacked and leaked online.

The suit against Toronto-based Avid Life Media alleges ALM failed to protect the privacy of "many thousands of Canadians" whose names, emails, home addresses and message history were posted online by hackers for public viewing.

"In many cases, the users paid an additional fee for the website to remove all of their user data, only to discover that the information was left intact and exposed," according to a statement by the lawyers.

Ashley Madison is known for its slogan: "Life is short. Have an affair." It helps connect people seeking to have extramarital relationships and is owned by Avid Life Media.

The lead plaintiff in the suit, filed by the law firms Charney Lawyers and Sutts, Strosberg LLP, is a disabled Ottawa widower.

His lawyers said he joined the website "for a short time in search of companionship" after losing his wife of 30 years to breast cancer.

But they added he "never met anybody in person from the site."

Canadian media in July reported that one in five Ottawa residents or nearly 200,000 people were registered with Ashley Madison, making the city the most infidelity-friendly in the country.

The Toronto Star this week identified hundreds of Canadian government email addresses in the leaked membership data.