Security tip: Avoid ‘Free Public Wi-Fi' connections

Sitting in your favorite coffee shop with your laptop, you decide you want to pop off a few quick e-mails to friends. You click on the wireless icon, hoping the coffee shop provides a free Wi-Fi network, and you get a list of possible connections. One says "free public Wi-Fi."

Sound good? It's not, and, if you use Windows, you shouldn't connect to this network. In fact, it won't even get you onto the Internet. It's actually just a computer-to-computer connection. It's possible the other computer owner doesn't even know he or she is offering "free public wi-fi" to the rest of the world. This ad-hoc network started at some unknown time and spread to any other computer that connected to it.

You might think that's relatively harmless, but if you connect this way to someone with malicious intent, your shared files could be compromised. And once you connect to this network, your computer will always make itself available to others around you.

That's why you should take steps to protect yourself from inadvertently connecting to such networks. Here's how:

If you're using Windows XP. It's easy to hide ad-hoc networks from your wireless card and, in case your computer has already been compromised, avoid further risk by disabling your laptop's ability to connect to them. In XP, open the "Network Connections" Control Panel, then right-click your wireless adapter and choose "Properties." Click the "Wireless Networks" tab, then the "Advanced" button. Click the choice for "Access-point (infrastructure) networks only", and make sure the checkbox below for "Automatically connect to non-preferred networks" is UN-checked, then close the window.

If you use Windows Vista. Go to Start/All Programs/Accessories, then choose Command Prompt. When the prompt comes up, type the following:

netsh wlan add filter permission=denyall networktype=adhoc

Now you're permanently protected from potentially harmful ad-hoc network connections.

If you use a Mac. By default, Macs don't connect automatically to ad hoc networks. And even if you do connect, it won't advertise itself later unless you explicitly create a network for it.

—Donna Tapellini and Dean Gallea