Diebold's ATMs, which run Windows XP, are the first ATMs to become infected with malware:
It is the first known case of a worm actually installing itself on individual ATM operating systems, says Peter Lind, a security expert at Spire Security in Malvern, Pennsylvania…
Diebold does not know how the worm got on to the closed financial network. But security experts suggest it could have been carried past security measure on an infected laptop computer. The laptop would have contracted Welchia while connected to the internet, and then transferred it when later connected to the financial network.
