What Is a Product Key?

How They're Formatted and Why You Might Need to Find Yours

Image of a Windows 8 Certificate of Authenticity
Windows 8 Certificate of Authenticity. © Microsoft
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The product key is a usually unique, alphanumeric code of any length required by many software programs during installation. They help software manufacturers ensure that each copy of their software was legally purchased.

Most software, including some operating systems and programs from most popular software makers, require product keys. As a general rule these days, if you pay for a program, then it probably requires a product key during install.

In addition to product keys, some software makers, including Microsoft, often require product activation to help further ensure that software is obtained legally.

Open source and free software programs usually do not require a product key unless the manufacturer implements its use for statistical purposes.

Note: Product keys are also sometimes called CD keys, key codes, licenses, software keys, product codes, or installation keys.

How Product Keys Are Used

A product key is like a password for a program. This password is given upon buying the software and can only be used with that specific application. Without the product key, the program will most likely not open past the product key page, or it might run but only as a trial of the full version.

Product keys can usually only be used by one installation of the program but some product key servers allow for the same key to be used by any number of people so long as they're not used simultaneously.

In these circumstances, there's a limited number of product key slots, so if the program using the key is shut down, another can be opened and use that same slot.

Microsoft Product Keys

All Microsoft Windows operating system versions require the entry of unique product keys during the installation process, as do all versions of Microsoft Office and most other Microsoft retail programs.

Microsoft product keys are often located on a product key sticker, an example of which you can see on this page.

In most versions of Windows and other Microsoft software, product keys are 25-characters in length and contain both letters and numbers.

In all versions of Windows since Windows 98, including Windows 10, Windows 8, Windows 7, Windows Vista, and Windows XP, product keys are of the 5x5 set (25-character) form as in xxxxx-xxxxx-xxxxx-xxxxx-xxxxx.

Older versions of Windows, like Windows NT and Windows 95, had 20-character product keys that took the form of xxxxx-xxx-xxxxxxx-xxxxx.

See our Windows Product Key FAQ for more information about Windows product keys.

Locating Product Keys

Since product keys are required during installation, finding that you've lost a product key could be a serious problem if you need to reinstall a program. Fortunately, you probably don't need to repurchase the software but instead just find the key you used when it was first installed.

The unique product key entered for an operating system or a software program is typically stored in an encrypted format in the Windows Registry, at least in Windows. This makes finding one very difficult without some help.

Luckily, there are special programs called product key finders that will locate these keys, so long as the program or operating system hasn't already been erased.

See our Free Product Key Finder Programs list for updated reviews of the best of these tools.

Warning About Downloading Product Keys

There are lots of online sources that either claim correctly that they have product keys you can use for various software programs, or claim erroneously that a program they provide can generate a product key for you.

The way they sometimes work is by having you replace a DLL or EXE file on your computer with one that was taken from a legitimate copy of the software; one that is using the product key legally.

Once the file replaces your copy of it, the program might now be a never ending "trial" or will work fully if you provide the given product key that goes with the pirated software.

Another way product keys are illegally distributed is simply through text files. If the software does all of the activation offline, the same code can be used by multiple people for multiple installations without raising any flags. This loophole is why lots of software programs activate their products online by sending the product key information elsewhere to validate it.

Programs that generate product keys are called keygen programs and they usually contain malware along with the product key applier/activator. This is one of the main reasons keygens should be avoided.

No matter how you go about it, getting a product key from anyone other than the software manufacturer is most likely illegal and considered software theft, and probably isn't safe to have on your computer.