EDIT: The replies indicate that my last sentence was unclear. Contrary to what it seemed to say, it meant that, since the voter registration isn't confidential, neither is the party information (except that sometimes the voter registration is confidential, as discussed in the article and my 'uncle' comment (https://news.ycombinator.com/item?id=10801570 )). Maybe I should have phrased it, equivalently but more clearly, as "that information is as public as the voter registration anyway".
The point of my comment was just that it is not true that "voters' parties weren't revealed", which I took to be part of dfc's comment (https://news.ycombinator.com/item?id=10801543 ).
Party registration is not private. It's public. Even if it was private in many states you can only vote in a primary with you are a registered member of that party which are then included in the voter registration lists.
The party affiliation data in the voter roles is probably one of the most heavily used fields in there to boot. A lot of petitions need to be signed by a certain number of registered party members -- the local party apparatus has to get signatures each (election) year to demonstrate that they are indeed the local apparatus for that party, individuals wanting to primary need a certain number of signatures to get on the primary ballot, you may also need to collect signatures to force an open (write-in) primary with no specified candidates...
Campaigns will also use it to target their literature; you might send one mailer to the members of your own party ("X is a totally loyal party member, here's seven things he did to support our core party values!"), another mailer to the opposition party ("X is not a total baby eater, here's five ways he crossed party lines to support things you probably care about!"), and a spattering of other mailers to the third-parties to emphasize support for their particular interests.
The weirder thing to me is that these databases also include birthdays. You could send birthday cards to everyone.
> This did not happen.
The list of fields at http://www.databreaches.net/wp-content/uploads/DataFields.jp... does include 'party', although I suppose that information is only as confidential as the voter registration anyway.
EDIT: The replies indicate that my last sentence was unclear. Contrary to what it seemed to say, it meant that, since the voter registration isn't confidential, neither is the party information (except that sometimes the voter registration is confidential, as discussed in the article and my 'uncle' comment (https://news.ycombinator.com/item?id=10801570 )). Maybe I should have phrased it, equivalently but more clearly, as "that information is as public as the voter registration anyway".
The point of my comment was just that it is not true that "voters' parties weren't revealed", which I took to be part of dfc's comment (https://news.ycombinator.com/item?id=10801543 ).