I assume you're talking about the app where you could find out if your neighbors were registered R or D. I don't think that info should be made public, but I can't find any evidence that the app was illegal. Can you clarify?
In most jurisdictions, you need to sign policy protections (and pay a fee, except parties get the full set for free) to get voter data in bulk. That data can't be redistributed except under tracked conditions. The app made it available to everybody.
Note that both Obama campaigns illegally distributed voter registration data freely and without qualification or tracking via their volunteer app.