What is a Certificate of Authenticity (COA)?
A Certificate of Authenticity (COA) is a label that helps you identify genuine Microsoft software. A COA is not a software license – it is a visual identifier that assists in determining whether or not the Microsoft software you are running is genuine. However, without it, you will not have a legal license to run Microsoft software. A COA should never be purchased by itself without the software it authenticates.
To help you verify the authenticity of the Microsoft software you acquired, be sure that your software came with one of the following COAs (or a previous version) and that the COA includes the advanced piracy prevention features described.