Necessary protection of wireless networks
A wireless network, and by extension a WiFi network, is much more sensitive than a wired network since data freely circulate in the air.
It is essential that you protect your wireless network, even if you think the circulating data are not confidential. An unprotected wireless network with no effort at configuration can make it possible for any user in your neighborhood (or upstairs or downstairs) to use your internet connection and possibly launch a certain number of attacks. As such, if a problem arises, the responsible party will be the owner of the internet connection, that is, yourself.
Before doing anything else, it is important that you follow some general instructions letting you guarantee a basic security level. The following article lays out a few general rules for protecting a WiFi network:
The rest of this article describes the manipulations that let you secure a WiFi network thanks to WEP or WPA.