The Conficker worm infected several hundred machines and critical medical equipment in an undisclosed number of U.S. hospitals recently, a security expert said on Thursday in a panel at the RSA security conference.

“It was not widespread, but it raises the awareness of what we would do if there were millions” of computers infected at hospitals or in critical infrastructure locations, Marcus Sachs told CNET News after the session. Sachs is the director of the SANS Internet Storm Center and a former White House cybersecurity official.

It is unclear how the devices, which control things like heart monitors and MRI machines, and the PCs got infected, he said. The computers are older machines running Windows NT and Windows 2000 in a local area network that was not supposed to have access to the Internet, however, the network was connected to one that has direct Internet access and so they were infected, he said. (CNET)