I've long recommended to my clients that they stay within Microsoft's life cycle with respect to their Windows operating systems. Most of them, even after explaining it, I suspect deep down they think it's a scheme to extort more money out of them to upgrade. Well, here's a perfect example to backup my claims.
This is why NO ONE should be running Windows 2000 or Millennium (ME) anymore (or earlier, i.e. 98, NT, 95, etc). The last sentence sums it up very nicely. Even with a current anti-virus subscription, you are NOT protected!
"Recently, the Conficker/Downadup worm infected several hundred machines and critical medical equipment in an undisclosed number of US hospitals. The attacks were not widespread; however, Marcus Sachs, director of the SANS Internet Storm Center, told CNET News that it raises the awareness of what we would do if there were millions of computers infected in hospitals or in critical infrastructure locations. It's not clear how the devices (including heart monitors, MRI machines and PCs) got infected. Infected computers were running Windows NT and Windows 2000 in a local area network (LAN) that wasn't supposed to be Internet accessible, but the LAN was connected to one with direct Internet access. A patch was released by Microsoft last October by November that fixes the problem, but the computers infected were reportedly too old to be patched."