OEM keys cannot be transferred to a different PC, so used ones are useless. OEM keys - Original Equipment Manufacturer keys are purchased by PC and laptop makers, such as Dell, to be pre-installed on a device before it is sold.They should only be used to activate copies of Windows within the terms of the MAK license agreement. MAK keys - Multiple Activation Keys (MAK) are part of a large bundle of Windows licenses sold to large companies by Microsoft.Where these keys originate from isn't all equally suspect, but the problem with buying from third-party websites or eBay sellers is you often won't know where it came from until it's too late to do anything about it. There are many places from which the cheap Windows keys you see for sale could have been obtained. But that doesn't completely absolve the buyer from blame. This side of the transaction is commonly the focus for software companies and law enforcement, rather than someone buying a single software key. Selling pirated or stolen software, particularly in bulk, is also very illegal. While prosecution for an individual is unlikely, purchasing stolen, pirated, or cracked software such as Windows 10 is against the law in most countries. The potential problems with the legality of buying cheap keys may occur if they have been obtained for sale through illegal means.