In October 2015, a Swedish tech blogger named Johny Krahbichler opened a package mailed from Warsaw: a DVD with a long alphanumeric code written on it, no return address, no explanation. When he played it, he found a two-minute black-and-white video of a figure in a plague doctor costume, standing in a ruined building, holding up a hand with a blinking light — set to loud, discordant buzzing.