No computer network is one hundred procent secure. It's always  possible for eavesdroppers to view  the traffic on any network, and it's often possible to add or introduce unwelcome traffic as well. Some networks are built and managed much more securely than others. For both wired and wireless networks alike, the real question to answer becomes - is it secure enough?

Wireless networks add an extra level of security complexity against to wired networks. Whereas wired networks send electrical signals or pulses of light through cable, wireless radio signals propogate through the air and are naturally easier to intercept. Signals from  wireless LANs (WLANs) pass through exterior walls of the building and into nearby streets or parking lots.

Network engineers and other technology specialist have closely scrutinized wireless network security because of the open-air nature of wireless communications.
The practice of wardriving, for example, exposed the vulnerabilities of home WLANs and accelerated the pace of security technology advances in home wireless equipment.

Overall, conventional wisdom holds that wireless networks are now "secure enough" to use in the vast majority of homes, and businesses. Security features like 128-bit WEP and WPA can scramble or "encrypt" network traffic so that its contents can not easily be deciphered by snoopers. Likewise, wireless routers and access points (APs) incorporate access control features such as MAC address filtering that deny network requests from unwanted clients.

Obviously every home or business must determine for themselves the level of risk they are comfortable in taking when implementing a wireless network. The better a wireless network is administered, the more secure it becomes. However, the only truly secure network is the one never built!