The Washington Post sheds some more light on what went wrong:
Shortly after 8 a.m. local time Saturday morning, an employee at the Hawaii Emergency Management Agency settled in at the start of his shift. Among his duties that day was to initiate an internal test of the emergency missile warning system: essentially, to practice sending an emergency alert to the public without actually sending it to the public.
Around 8:05 a.m., the Hawaii emergency employee initiated the internal test, according to a timeline released by the state. From a drop-down menu on a computer program, he saw two options: “Test missile alert” and “Missile alert.”
This sounds like terrible user interface design to me. Why have the genuine “Jeez Louise! Freak out everybody!” option slap-bang next to the harmless one labelled “Test the brown alert”?
Even though the menu option still required confirmation that the user really wanted to send an alert, that wasn’t enough, on this occasion, to prevent the worker from robotically clicking onwards.
How on Earth were those buttons next to each other? And why can just one person send an alert like this to millions of people? And, finally, why weren’t the local authorities authorized to send out a retraction of this alert for thirty-eight minutes?