http://www.diariodemexico.com.mx/inemexico-encuentra-quien-f...
The government isn't publishing details, but the article gives the impression that it was some Mexican political party acting out of line who should not have uploaded this data to US servers. It appears that each party receives a copy of electoral registrations.
¿Qué chingados? I didn't know every party got a copy of all voter registrations. This seems grossly undemocratic.