... someone messed up big time and the financial data of 4.5 million visitors and over 1000 travel agencies have been exposed.
This has been all over the news today: https://www.elconfidencial.com/tecnologia/2019-05-22/alhambra-hiberus-sicomoro-patronato-generalife-junta-andalucia_2013846/
The software giant Hiberus, responsible for the software of the ticket sales of La Alhambra (and other clients) hasn't yet commented... but its website is today, suspiciously, offline "under maintenance". Its spin-off, Sicomoro, the one actually managing the sales, has simply stated that "any such error has been properly addressed and is currently no longer existing".
The new software, by which you can print a QRcode at home and save queuing at La Alhambra had been just launched last October: https://www.20minutos.es/noticia/3233634/0/nuevo-sistema-venta-entradas-alhambra-acaba-colas/
To my understanding, this does not affect any reservation you might have. However, if you purchased your ticket within this timeframe, it's worth notifying your bank you ccard "might have been" compromised, just in case.
Just sayin'.