A reasonably good protection can be reached by defining WEP (Wired Equivalent Privacy) or WPA (Wi-Fi Protected Access).
WEP - short for Wired Equivalent Privacy, a security protocol for wireless local area networks (WLANs) defined in the 802.11b/g standard. WEP is designed to provide the same level of security as that of a wired LAN. LANs are inherently more secure than WLANs because LANs are somewhat protected by the physicalities of their structure, having some or all part of the network inside a building that can be protected from unauthorized access. WLANs, which are over radio waves, do not have the same physical structure and therefore are more vulnerable to tampering. WEP aims to provide security by encrypting data over radio waves so that it is protected as it is transmitted from one end point to another.
WPA - short for Wi-Fi Protected Access, a Wi-Fi standard that was designed to improve upon the security features of WEP. The technology is designed to work with existing Wi-Fi products that have been enabled with WEP (i.e., as a software upgrade to existing hardware), but the technology includes two improvements over WEP:
- Improved data encryption through the temporal key integrity protocol (TKIP). TKIP scrambles the keys using a hashing algorithm and, by adding an integrity-checking feature, ensures that the keys haven’t been tampered with.
- User authentication, which is generally missing in WEP, through the extensible authentication protocol (EAP). WEP regulates access to a wireless network based on a computer’s hardware-specific MAC address, which is relatively simple to be sniffed out and stolen. EAP is built on a more secure public-key encryption system to ensure that only authorized network users can access the network.
You have now to check what of the two security protocols is supported on all your wireless clients. This is what you can get. It's not possible to run both security protocols at the same time.
Furthermore i suggest to use MAC filtering. In the router setup program you will find it under the Tab "Wireless" and there you have to enter all MAC addresses of all wireless clients in your network. MAC addresses are printed on the sticker of every NIC (Network Interface Card).
Most important is for sure you change your router password, so no other person can get access to it and change your settings.
And finally to have running all fine, the SSID (Service Set Identifier) have to be the same on the router as well as in all wireless clients.
Happy wireless networking ;-)