Arizona's voter database has apparently been tampered with or at the very least been susceptible to lax security standards.

Apparently someone has copies of voter registration forms and just copied the signature and changed party affiliation, nullifying votes (causing voters to receive provisional ballets, which generally are not counted) https://www.youtube.com/watch?v=P1PnM6rf7X8

Here's the Arizona House elections Committee hearing, and a citizen mentions that voter registration documents have been leaked to the web. https://youtu.be/ESyXvGLMIS0?t=58m37s