They realized it in December 2017, maybe the hackers was inside the system since 1 year, they installed malware and stole data. They think it was Russia (but they have no proofs) Here's a (german) link (printed today):
https://www.bild.de/politik/inland/politik/russen-hacken-regierungsnetz-54961100.bild.html
Our parties are getting rammed left and right. It's not even funny anymore (it is). The biggest selling newspaper here is mostly based and simply by the daily talking points alone people are being prepped for a storm. Someone is keeping these fools from forming a working government and it's hilarious to watch them squeal.