This is an interesting question, particularly when it comes to understanding “IP-changing” services.
First, I need to clear up some terminology to be sure we’re talking about the same thing.
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ISP versus IP
In your question, you say that you’re “using an ISP-changer program.” I think you mean IP, not ISP.
Your ISP is your Internet Service Provider. They’re the company from which you get access to the internet, and to which you connect your computer and other internet-enabled equipment.
When you connect to a site or service online — even something as simple as a website such as Ask Leo! — that site’s servers have access to the IP address from which you connected: your IP address. This is required so the server knows where to send the data you requested.
You can use programs or services to make it look like you’re coming from a different IP address — what I think you’re referring to as a “changer”. Instead of your own home IP address, the remote service sees something else. For example, the Ask Leo! server would see the IP address of this changing service, rather than yours.
You haven’t changed your ISP at all; the same company still provides your internet connection. You’re not really changing your IP address either, as you’re still connected to the internet using the IP address assigned by your ISP.
The only thing that changes is the IP address that you appear to be at, as seen at the other end of the connections you make.
It sounds like I’m being pedantic, but when we talk about things like security, we have to use correct terminology to make sure that we’re talking about the same thing.
A more correct way to phrase what you’re attempting is: you want to hide your IP address as you use the internet.
Different approaches to hiding your IP address
When it comes to hiding your IP address, there are three different approaches2.
Proxies. These are services that you connect to normally that then make all subsequent requests on your behalf. You may have seen proxy configuration options in your web browser, and indeed, they are typically limited only to handling web-browsing traffic. Other than configuring the proxy in your browser, there’s no additional change to your system. In practice, they’re rare outside of the corporate environment.
VPNs. These services act similarly to proxies, except they handle all of your internet traffic. This requires that you install or configure a VPN service in your operating system, not just your browser. When you connect to anything on the internet, that request is sent first to the VPN service, and from there makes its way to whatever site or service you’re trying to use. To that site or service, you “look like” you’re coming from the VPN’s IP address, not your own.
TOR. This is, in a way, a special case of a VPN, or perhaps a proxy on steroids. It is specifically targeted at web browsing, though I understand it can be used for other things. Rather than being a single server or service, you install a special browser, and your traffic is routed through a series of semi-randomly selected intermediate nodes until it reaches its destination. To the destination site or server, it “looks like” you’re coming from the last node in your path, referred to as an exit node.
In all three cases, you still connect to the internet using your IP address, but each has a different impact on how easy it is to see your IP address and the data you’re sending and receiving.
So your question might be further refined to “Can my ISP see that I’m using a VPN, proxy, or TOR?”
The answer, surprisingly, is yes. But what may matter more is what else they (and anyone in between) can or cannot see.
Who sees what
Exactly who sees what depends on the service you’re using.
- Your ISP can see you’re using a proxy, and what specific proxy you’re using. Depending on the proxy, your ISP may even be able to see the sites and services you’re visiting, and in the worst case, the data you’re sending and receiving.
- The site or service you’re visiting can see your data, of course, but will see only the IP address of the proxy.
- The proxy service can see everything: your IP address, who you’re connecting to, and the data you’re exchanging. While normally that doesn’t include data encrypted using https, in the case of some corporate proxies, it may.
- Your ISP can see you’re using a VPN, and what specific VPN service you’re using; that’s all.
- The site or service you visit can see your data, of course, but will see only the IP address of the VPN.
- The VPN service can see almost everything: your IP address, who you’re connecting to, and any unencrypted data you’re exchanging.
- Your ISP can see you’re using TOR, and how you are connecting to the TOR network; that’s all.
- The site or service you’re visiting can see your data, of course, but will see only the IP address of the TOR exit node.
- The last node in your data’s path across the TOR network can see who you’re connecting to and any unencrypted data you’re exchanging. Intermediate nodes cannot.
What your ISP still sees
As I mentioned, your ISP can generally see that you are using one of these services. In most cases, they cannot see what websites or other services you connect to through these services, however.
What your ISP can see, however, is how much data you’re transferring. They may not know what it is, but if you’re downloading a lot, they’ll certainly see that it’s a lot.