The history of spectacular hacker attacks has a notable new chapter: The hotel chain Marriott recently had to admit that hackers successfully attacked the guest database of their subsidiary Starwood. The perpetrators stole personal data such as birth dates, addresses, passport numbers and even credit card information from 327 million guests. The attackers had been active since 2014 and were only discovered at the beginning of November 2018. The Marriott share price crashed after the attack became known. The attack shows once again the risk IT security problems pose for large companies – and how difficult it is for companies in everyday life to secure their complex IT infrastructures, some of which are networked across subsidiaries.