It implies much more than just your address.
It all depends on how they got your IP address and whether it’s really yours at all.
At least one scenario represents a serious security risk, but there are also situations in which it’s not really an issue under your control.
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My neighbor and my IP address
- The only way your neighbor can truly be using your IP address is if they have access to your local network.
- The most common scenario is that they’ve connected to your open wireless hotspot. Secure the hotspot by adding a wireless password.
- It’s also possible that your IP address has changed, and was once theirs.
- It’s very easy to misread IP address information, depending on your source.
- Malicious software on your machine could also be sending email appearing to be from your neighbor.
It implies they’re on your network
If your neighbor is truly using your IP address, it implies they are connected to your network.
That’s a bad thing, unless you trust them and have explicitly allowed them to do so. I’m guessing from your question that’s not the case.
The most common reason is that you have an open wireless hotspot.
- You have a wireless router or access point.
- The wireless connection is not password protected.
- Your neighbor is in range and is using it.
Your neighbor could be completely unaware. It can happen accidentally if they’re not paying attention to what they’re connecting to. I would not assume malicious intent unless you have information that says otherwise.
The fix is very simple: password-protect the wireless connection. Configure the wireless access point to use WPA2 or 3, which requires a password to connect.
No one except those you’ve authorized will be able to connect to your network.
As a bonus, your connections will be encrypted and no one will be able to “sniff” them (as is possible at most free wireless hotspots).
There are a few other reasons your neighbor might appear to have sent email “from” your IP address.
You could have misread the email headers. Your IP address, as the destination when you download your email, may appear within it, in addition to the IP and email address the mail was sent from.
You and your neighbor could have IP addresses assigned by the same ISP. This has two interesting ramifications:
- Your IP address could be very similar to that of your neighbor. Even a single-digit difference means it’s a different IP address. Read the IP addresses carefully.
- IP addresses can change; your IP address today could easily have been your neighbor’s IP address yesterday, when they were sending email.
The email might not be from your neighbor at all. Your machine could be infected with a spam-sending virus or bot, and it could be spoofing the “From” address so as to appear that it was sent by your neighbor.
Changing your IP address
Can you change your IP address? Well, it depends.
First, if you’ve been assigned a static (unchanging) IP address, you’ll need to contact your ISP and coordinate changing it with them.
If you have a more common dynamic IP address (if you don’t know, then it likely is), you can try to change the address by unplugging your internet-connected modem and/or router, waiting awhile, and plugging it back in again. This causes it to “ask” for a new IP address.
The problem here is that there’s no way to force the newly assigned address to be different than whatever you had before. Many ISPs try to give you the same IP address for “a while”, even when you’re not connected for a time, as it can be slightly more efficient for them.