What is a certificate of authenticity (COA)?

A certificate of authenticity, or COA, is a proof of purchase that is provided with certain products. Most Microsoft® products, including their Windows® operating systems and office suites, come with one. Other software manufacturer's, like Corel, provide COA documents with their office suites as well.

A COA normally appears like a formal certificate with typical, hard-to-copy green swirl patterns around the edges to help indicate it is a legitimate certificate. It provides the name of the product it certifies and usually provides a certificate number, product key or serial number for the product.

Depending on the product, a COA may come as a sheet of paper, a small card or as a sticker label attached to a manual, CD case or even to the computer. The Microsoft Windows operating system COA is provided as a sticker attached directly to a Dell computer (Figure 1).

Figure 1 - Example of a Microsoft Windows COA label attached to the bottom of a Dell portable computer.