Using a wireless encryption key i.e WPA (Or less secure WEP) and MAC Address filtering.
You can also stop the broadcasting the SSID, however the wireless access point can still be picked up.
SSID broadcast must be off, wireless security must be on (WPA at least). You might want to enable MAC filter too.
Secured networks, MAC tables and so on.
It uses a 128-bit pre-shared hexadecimal key to prevent unauthorized wireless access.
This is assuming that there is no outside access to the Ethernet network such as a Internet connection. If there were then firewalls would be needed to prevent a outside intrusion of the network. In addition to physical access security, a wireless network requires authentication and encryption to prevent unauthorized devices from connecting to the wireless network or capturing and decoding the data that is being transferred via a wireless network connection. If the wireless network has outside WAN access then you would also need firewalls as with the Ethernet network.
firewall
use wireless encryption. for example, WPA or WEP (http://en.wikipedia.org/wiki/Wifi#Network_security)
most pepole would says yes as you may want to do personal banking and such and is someone has access to your network you can be prone to someone peeking in to what you do online
to prevent unauthorized persons from gaining access to a private network
To prevent collisions.
loro maro = Firewall
Disabling the SSID Broadcast.
Ssid broadcast
It is prevent all connected network cards sending at the same time.
Use any of the WPA or WPA2 or WEP etc. wireless network security methode. Also, MAC address filtering is a really effective methode, with which you can tell your w/l access point to strictly allow connections from only pre-specified devices.