If you have a wireless network, you must make sure it's secure: without proper security precautions, it's very likely your computer network can be compromised. Many applications exist for mobile devices that automatically search for vulnerable wireless networks and then automatically crack their way in. The vast majority of these programs are used simply to gain free access to the internet by people trying to save money on their mobile phone bill, but even still, there's nothing stopping them from trying to snoop around your network once they've cracked their way in. Nothing stops their virus-infected laptop/mobile device from trying to spread into your computers either (a proper anti-virus program should catch these, but it's not guaranteed).
Informative Technologies can configure your wireless network to prevent unauthorized access to your systems.