How do websites know if you're running on a VPN?

Question

I've noticed that various websites know when you're running through a VPN, and they refuse to let you login or even sometimes access their website if you are doing so. How would they know that you're going through a VPN?

Answer 1

I don't have all the answers but a couple of possibilities are:



1) They have lists of known VPN providers



2) They run a script on your system to identify the software (VPN) you are using



3) They run scripts on your system to detect your actual "public" IP address provided by your ISP. Any mis-match means you are likely using a VPN





There are other, more technical ways as well, but someone else may have to explain those better...

Answer 2

It's not the VPN that they detect, but the proxy server that the VPN connects a user to.



If a website gets lots of connections, from different users with different home addresses all connecting to the site from the same IP address (the address of the proxy site), the site 'knows' it's not your real IP address. The website cannot tell whether your connection to the proxy is normal or via a VPN.

Answer 3

An alternative to disguising your computer by running software in it to do VPN, you could get a router that does the VPN routine, connects to the VPN provider.  Your computer is unchanged.

I use that and it works fine.  Not every router can do that--some need the BIOS refreshed.

Answer 4

VPNs require that a computer is running at some other location so that you can appear to be at that location. They require someone operates the software, which generally means there's a company on that end. That company has only a limited number of IP addresses associated with it and even if it's a million, computers are pretty good with numbers.



In any event, all that means is that you take note of every IP address for every VPN software you can find and blacklist them. If you're a big company, such as Netflix, you can just find a way to get a subscription to every VPN company who has an endpoint in some area for a month or so. It's not that unreasonable.



There are probably easier ways, but this just shows that even with a minor investment, you can find out who the VPNs are.