Google your router make and model, such as "belkin wrt54g login information page" from there you can login using the router default password. From there look for a security section and you can usually select a few different forms of protection, "Wep" is just one of them, basically click the type of service you want and enter a password. Then next time anyone wants to connect to your wifi they will need to put that password in to connect.
2nd thread ?
you already got good advice in the 1st one me thinks, but to sum it up again:
- get a new router/modem with at least wpa2 & eas encryption
- change your private/hidden network ssid & passwords regularly (long pw's, with mixed letters+numbers+characters)
- set your router to accept/forward only your 2 computer's mac addresses
- turn off wifi when not needed
- check the hardware ports on your computer devices for unknown usb dongles (which your neighbor probably could've put there to collect data ?)
even with all of the above, it will always be possible to sniff packets & hack someone's wifi when time and hardware is at hand. even a small laptop with a powerful graphics card can do the trick in a few hours!
so try to make it as hard as possible