Around March 24, researchers monitoring the worm noticed that an imaging machine used to review high-resolution images was reaching out over the Internet to get instructions — presumably from the programmers who created Conficker.

The researchers dug deeper and discovered that more than 300 similar devices at hospitals around the world had been compromised. The manufacturer of the devices told them none of the machines were supposed to be connected to the Internet — and yet they were. And because the machines were running an unpatched version of Microsoft’s operating system used in embedded devices they were vulnerable.