Ontario's chief electoral officer announced this week that two memory sticks containing copies of personal information collected from voters in 20 to 25 ridings went missing in April.
The lawsuit seeks, among other things, financial compensation for any individuals whose personal information has been lost.
Steve Osborne of the Merchant Law Group says there's a substantial risk that the personal information of millions of voters could be used for identity theft or other frauds. Allegations made in the suit have not been proven in court.
Because Elections Ontario doesn't yet know which ridings from a pool of 49 were affected, they've had to warn millions of voters about the breach.
Ontario Provincial Police are investigating the breach, along with Privacy and Information Commissioner Ann Cavoukian.
Cavoukian called the breach "massive," adding that the number of people involved was huge — "larger than the size of most provinces."
The USB keys contained the names, birth dates, addresses and gender of voters, said Greg Essensa, Ontario's chief electoral officer.
The data doesn't include social insurance numbers, health card or driver's licence information, phone numbers, email addresses, credit card or banking information.
Osborne said a major concern is that the data isn't protected.
"One of the most serious concerns about this situation is the fact that Ontario Elections admits that the two lost USB keys were not encrypted or password-protected," Osborne said.
The lawsuit was filed with the Ontario Superior Court of Justice on Friday. The allegations have not been proven in court.
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