From CBC News:
Elections Ontario has discovered a privacy breach that involves the personal information of voters in up to 24 provincial ridings.
CBC News has learned that memory sticks containing personal information about voters have gone missing from the office of the chief electoral officer for Ontario.
The information on the missing memory sticks includes the full name, address, gender and birth date of voters and may also include information on whether or not these same individuals voted.
Read more on CBC News. The story says the data were encrypted, which means this may not be a breach at all, by most definitions. An investigation is under way.
UPDATE: Now it seems like the data were NOT encrypted. Oh boy.