The other major aspect of security you want to take into account is the network you are using for communication with the outside world. Is your home wireless network secure? Is it using WEP or WPA or WPA2? Are you regularly using insecure networks at hotels, airports, coffee shops?
The first thing you want to do is lock down your wireless network since that is probably where most of your computer activity takes place.You want to enable security and choose the highest possible security. Check out my article on which WiFi encryption protocol is best.
There are also a lot of other things you can do, such as:
A - Disabling SSID Broadcast
B - Enabling MAC Address Filteirng
C - Enabling AP Isolation
You can read up online about these other types of security. The second thing you want to do (actually maybe the first) is change the username and password used to access your wireless router. So it’s great if you setup WPA2 with AES, but if someone just types in the IP address of your router and can login using the default username and password for the router (which can be found on the Internet in seconds), then they can actually change everything and lock you our of your own router!
Luckily, you can always reset your router and gain access, but it’s still very risky because someone can log into your router and then access everything else that is connected to your network. Logging into the router is nice because it can tell you all the clients connected to the router and their IP addresses. It’s never a good idea to buy a new wireless router, bring it home and just connect it up without setting up the security on it first.
Lastly, it’s definitely necessary to enable the firewall on your router and your computers. This will prevent applications from communicating on certain ports on your computer.
"Computer Tips Step 4 – Secure Your Network"
Reference : online-tech-tips.com