Is There Really Any Way to Uniquely Identify Any Computer at All

What's a good way to uniquely identify a computer?

Another solution is to use a licensing technology with a dongle. This is a small device that plugs into USB or another I/O port on the host, and serves as a unique, physical key to activate the software.

A third solution is to provide a license manager. That is, when the software starts up, it queries a server on the network (either on the customer's LAN or else accessed at your company via the internet) that validates that the customer's usage of the software is legitimate. This is a good solution for "concurrent licenses" so customers can install your software on many hosts, but you license it for simultaneous use on a limited number of hosts. FLEXnet Publisher is an example of a license management solution.

The MAC address of the network card is the solution I used last time I worked for a company that licensed software to run on a specific host.

However, I want to offer a caution: if you do this type of licensing, you have to anticipate that it'll become an ongoing administrative chore to track your customers' licenses. Once you have a few hundred customers, you'll be amazed at how frequently you get phone calls with requests to change keys

"We upgraded our server to a gigabit
network adapter, and now the license
won't work because the new adapter has
a different MAC address."

Or else the customers may replace their whole machine, and need an updated license to run your software on the new machine. We got these calls practically every day at the company I worked for.

You also need to trust the customer to stop using your software on the old computer (or network adapter) if you give them a new key. If you couldn't trust them to obey the license in the first place, how can you trust that they'll throw away the old key?

If you don't plan how you're going to support this administrative activity, don't license your product in this way. You'll only inconvenience your good customers, who would have cooperated anyway.

Is there really any way to uniquely identify any computer at all

The fact in getting a globally unique ID is, only MAC address is the ID that will not change if you set up your system all over. IF you are generating a key for a specific product, the best way to do it is assigning unique IDs for products and combining the product ID with MAC address. Hope it helps.

how can I Uniquely identify a computer

The usual approach is to give each client a login (name + password). That way, it's easy to replace clients when they need upgrade or when they fail.

MAC address should be unique but there is no central registry which enforces this rule. There are also tools to change it, so it's only somewhat reliable.

CPU and HD IDs are harder to change but people will come complaining when their hard disk died or when they upgrade their system.

Many PCs have TPM modules which have their own IDs but they can be disabled and the IDs can be wiped. Also, there are privacy issues (people don't like it when software automatically tracks them).

Another problem with an automated ID approach is how to identify them on the server. When several clients connect for the first time in quick succession, you will have trouble to tell them apart.

What is a good unique PC identifier?

Some good identifiers:

MAC Address: It's fairly easy to get at, and it's usually unique. However, it can be spoofed/changed rather easily, so it depends on how unique it needs to be.
CPU Serial Number: It's not available on lots of older systems, but it's there. Check out this MSDN page. It won't change, but it's bound to a computer.
HDD Serial Number: It's likely to not change, but can be a nuisance if the HD fails. Check out this MSDN page.

How to uniquely identify computers that access a website

There is no reliable way to uniquely identify a browser, because there is nothing that prevents two computers from having the exact same configurations (operation system, browser, location, cookies, flash configuration, etc).

The best that we can do is to gather as many information about the browser as possible. This is well-known approach called browser/device fingerprinting. Although the result is not perfect, it is quite good. Browser's fingerprint typically includes browser name, operating system, fonts, plugins installed, etc. You can test how unique your browser is using https://panopticlick.eff.org/.

Uniquely identify one computer

You can set a cookie. This will be remembered by the client and transmitted to the server as part of every request. More information here: http://www.w3schools.com/PHP/php_cookies.asp

Is an ASHWID guaranteed to uniquely identify a device?

No, the ASHWID is not guaranteed to uniquely identify a device. At work, I've seen dozens of daily collisions where one monthly is our tolerance.

Further, the ASHWID might frequently change for the same device -- since Windows 8 will often run on laptops that might add a docking station, USB thumb-drive, or a plug-in Bluetooth adapter. The best use of the ASHWID is for verifying that a user has only installed your app to a limited number of devices, and you do that by parsing the ASHWID and selectively comparing it to previously-seen ASHWIDs from that user.

As for a unique hardware identifier, I suggest an MD5 digest of a string containing multiple components, of which some components of the ASHWID can play a part.

You might randomly generate a large number (64+ bits) and store that (eg in the registry). And of course the user's login name/ID should be unique to that user, if you want something else to include in a hash. You also need to consider what you want to do if the user clones an OS install, or replaces the HD after a drive failure.

Back in the Windows Desktop world, I used the MachineGuid registry key and the serial number of the boot device, but I'm fighting to get access to that info in a Windows Store app. If you have access, MachineGuid is in HKLM\SOFTWARE\Microsoft\Cryptography, which MS guarantees to be unique. The serial number of the boot device ::GetVolumeInformationW(::SHGetFolderPathW(~),~) will be fairly unique but only 32 bits.

How to uniquely identify computer using C#?

How about the MAC address of the network card?