Block someone from using your wifi

Really depends on your router. If you have your own wireless router and are somewhat technical, you should be able to go into the admin settings page and simply deny his computers MAC address from connecting to the router.

If you rent a modem/router combo from Cox, you may not be able to do that, they block a lot of features to make them "easy to use". In that case you would have to change the wifi authentication key (password)

Depending on your router, you may be able to block his MAC address but ... that blocks one device only.  If he knows your password he can always login from another device.  Your best bet is to change the password, I know it's a pain but it's your best option.  Also, be sure you are using WPA2-AES encryption.

Honestly?  Change the password.  The only way to block him is to block his MAC address, but with some adapters he can easily change the ID and reconnect.

Just like trying to stop a burglar from getting into your house if he has the key - you change the lock.  Anything else won't stop them.

I would want to know how the "friend" connected to your Wifi to begin with. Did you give him the password? Also, if he is your friend, why can't you ask him to stop and go away? If changing the password doesn't work, get the HOSE! 

"Blocking" someone is insensitive and unacceptable!  You need to be more inclusive.  You must welcome people of different ethnic, cultural and economic backgrounds not only in front of your house but onto your network.

Before I reply emotionally to that comment, I would like to know it's intent. Was it a attempt at political satire? Because if your network belonged to the entire country, I would agree. However, it does not, so your comment is so ridiculous that I fear I must be misunderstanding it.

Also, my comment was not meant to be confrontational/political. My point was why go through the trouble of blocking him from the network when you can get him to leave the property.

grymwulf said:

Honestly?  Change the password.  The only way to block him is to block his MAC address, but with some adapters he can easily change the ID and reconnect.

Just like trying to stop a burglar from getting into your house if he has the key - you change the lock.  Anything else won't stop them.

@grymwulf, in a previous thread you said just the opposite...  "The only truly effective way to prevent other people from accessing your Wifi is to change the wifi pre-shared key (password/passphrase)".  Which is it?  Or is the answer just the opposite of what others post?

There is another sure-fire way to do it without changing the password.....depending on your router.  Most routers have a section in the setup to block a specific MAC address.  But as someone else said, that person could connect with another device.  The other usual setting is to "allow only these devices" or something titled similarly.  That is what I use.  It takes a few minutes to get the MAC address of your devices and enter them, but once you do that, there should be no way for another device to get into your network regardless of whether or not they have your password. 

Davidoo said:
here should be no way for another device to get into your network regardless of whether or not they have your password. 

That isn't quite true. While it would be harder, a wifi snooper program can pretty easily pick up the MAC addresses of other wireless devices on your network and then the attacker can clone their MAC address to be the same and wait for that device to disconnect from the network. MAC address filtering of any kind is not a security measure IMO, it is a network management tool. 

If you read my entire response, I said you can block them using MAC address blocking, but it is trivial to bypass that.

And the phrase after it, saying 'change the lock' is to change your wifi password - and 'Anything else won't stop them'.  Please read and understand the entire response before judging.  I don't tend to use the exact same wording each and every time - I tend to explain things in different ways on different days.

And it appears I used two different wordings to refer to the same thing.  MAC addresses are also considered MAC IDs, so when I said you could block with the MAC address, but he could change his 'ID' to bypass that block, I should have typed he could change his MAC address to bypass the block.