95% of the world's ATMs run on Windows XP

"Inside every ATM casing is a computer, and like all such devices, each one runs on an OS. Microsoft’s 12-year-old Windows XP dominates the ATM market, powering more than 95 percent of the world’s machines and a similar percentage in the U.S., according to Robert Johnston, a marketing director at NCR (NCR), the largest ATM supplier in the U.S."
Source:  Bloomberg, 16th January 2014