Target was hacked because they were flagrantly ignoring basic security procedures, like "making your POS systems available on the same network you use for everything else." [1]

Blaming the Target break-in on the OS security is like having unprotected sex in the back of a Buick, and blaming GM for the STD you contracted because it would've happened if the car hadn't had such a roomy backseat.

[1] http://www.computerworld.com/s/article/9246074/Target_breach...