ZDNet: Tech Update: Platforms/OS / Know the rules: Reimaging Windows

Microsoft's Reimaging Rights: What Is and Isn't Allowed

Although Microsoft now allows most enterprises to reimage their Windows workstations without having to pay an additional fee, it's not an "anything goes" proposition, and some enterprises appear to be bending the rules in their use of reimaging, which could result in license compliance issues in the future.
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