What is the Windows Certificate of Authenticity?

The Certificate of Authenticity (COA) is a special security label that accompanies legally licensed Microsoft software to help prevent counterfeiting. If you see the COA on a Microsoft software box, you know that the software and other items inside, such as media and manuals, are genuine. If your computer came with Windows already installed, look for the COA on the outside of your computer. If you have a small device (with a length or width of 6 inches or less), the COA might be under the battery.