6sigmasoftware at www.6sigmasoftware.com is not a Microsoft authorized reseller of Windows and office activation keys. Some websites sell volume license keys which are meant to be used with multiple keys, but they can be invalidated at any time and are not legal. So, be careful of where you get your licenses or you'll risk facing problems down the line. Those volume license keys may work for a month or so, may not work, or have expired. And, if the keys work, once Microsoft detected that these keys are being abused, they will block them from further use, which will cause them to stop working. This why it is recommended that you purchase genuine licenses from the Microsoft Store.