How do I block someone in my neighbourhood from hijacking the SSID of my wifi every time I change it

They're probably running what's known as a Pineapple, or some similar device that implements the Evil Twin. I've encountered such devices in use, and they're all vacuuming up credentials. It's not fun to deal with these.

This is a limitation in how most systems — not just OS X — access Wi-Fi networks, so you can switch to WPA2 or hidden or whatever else, and it won't help.

The only way you might avoid this is to use a wired connection, or to avoid storing the password for your Wi-Fi network, and enter it each time. See this and this.

Blocking by BSSID will not work because it's trivial to spoof a MAC address as well. Take Linc's advice and call the authorities. It's likely that a knock at the door by police or the FCC will stop the issue cold -- particularly if it's a young kid that's just messing around and doesn't understand the repercussions.

You are likely the only one in the neighborhood that has recognized the attempted attack. You may have many neighbors that are unwillingly falling for it and may now be subject to man in the middle attacks. There are many good articles on the web about evil twin attacks, including why it's critical to disable the iOS "Ask to Join Networks" setting so your iOS device does not join fake ISP and carrier networks of known names.

What you're describing is called an "evil twin attack." It's most likely illegal and should be reported to the responsible authorities. There is no easy way to defend against the attack. Changing your network password won't work, because the rogue access point can be configured to accept any password, which it will then steal.

rupertjones wrote:

It is. This situation is about mac os only connecting to the strongest SSID. This person is clearly using this shortcoming to hijack my SSID and try and hack my computer. I need to block them by BSSID/mac code. Surely this can be done?

They can't hack your computer without installing something on it remotely or physically getting their hands on it. To do the former, you'd have to download something they sent to you and then install it on your computer. I don't think you're negligent enough to do that. Being a punk and changing their network name to yours isn't enough to get them inside your system. So I don't think you need to worry about that.

In order to block their MAC address from accessing your network, you need their MAC address first. Obviously. Can't block something if you don't have it. I don't know what make/model your router is, but I believe these instructions for not only finding the MAC address, but then blocking it, should work.

http://blog.dlink.com/qa-whose-are-those-unknown-devices-connected-to-my-network -2/

Wireless security WPA2 Personal

If you are using a Apple router you can use the Airport Utility.app to create a hidden Network.

~/Application/Utilities/Airport Utility.app>click on your router>Edit

>Wireless>Wireless options>Create a hidden Network

There is no tool in OS X to do that.

Consider this approach instead:

• Create your new SSID. Passcode protect it (WPA, WPA2, etc.). Join it immediately.
• On your Mac, go to System Preferences > Network > Advanced. Check "Remember networks this computer has joined."

Your problem is a matter for law enforcement. I don't advise trying to beat an illegal hacker at his own game. If you don't think the local authorities will take action, I suggest you get in touch with the FCC (if you're in the U.S.) or the equivalent national agency regulating radio communications.

Making your network hidden won't have the slightest effect.

If you blocked it, you'd be blocking your own access point as well. Every access point ever made is supposed to have a globally unique and permanent ID in its firmware. The hacker is breaking that rule.

Is your Wi-Fi network password protected? What type of password protection are you using?