MrSeb writes: "Bad news: With an Arduino microcontroller and a little bit of programming, it’s possible for a hacker to gain instant, untraceable access to millions of key card-protected hotel rooms. This hack was demonstrated by Cody Brocious, a Mozilla software developer, at the Black Hat security conference in Las Vegas. At risk are four million hotel rooms secured by Onity programmable key card locks. According to Brocious, who didn't disclose the hack to Onity before going public, there is no easy fix: There isn’t a firmware upgrade — if hotels want to secure their guests, every single lock will have to be changed. I wish I could say that Brocious spent months on this hack, painstakingly reverse-engineering the Onity lock protocol, but the truth — as always, it seems — is far more depressing. “With how stupidly simple this is, it wouldn’t surprise me if a thousand other people have found this same vulnerability and sold it to other governments,” says Brocious. “An intern at the NSA could find this in five minutes.”"