Multiple security advisories and public research reports show that all three of the controller models reportedly hacked in the incident—sold by Danfoss of Denmark and Dixell and its parent company Copeland in the US—contained critical vulnerabilities that allow attackers to remotely log in to the devices with the same system rights as administrators. Until recently, Danfoss controllers, for instance, used a credential that changes each day. The password is generated by the publicly available firmware based on the date. A hacker who takes the time to analyze the code can do the same thing on any device that hasn’t received a recent update. Daily passwords are identical across models located in hundreds or thousands of stores.

A raft of critical vulnerabilities fixed in the past few months in Copeland/Dixel controllers also give similar remote access.

Besides running controllers with outdated firmware, the affected stores likely also failed to put the devices behind a VPN and create a restricted list of IP addresses allowed to log in. These protections are standard but often not followed. In this case, that failure enabled a mass hack that likely cost tens or hundreds of millions of euros. Spain, Portugal, Poland, Germany, and Belgium were also reportedly affected.