I like the idea of keeping a Wi-Fi network open so visitors can be welcomed into the warm Internet like Elijah to a seder. But for your business, you'll likely want restrict access as much as possible to minimize the risk of stolen data. A Wi-Fi network without a password sends information in-the-clear, meaning that anyone nearby can read it. Here are several ways to close your network's windows to keep pests out.

Set a password. If your network is open--it doesn't require a password--all of the data flying through the air is just like shouting across a party. Anyone who wants to listen can hear your conversation. Encrypt the transfer with a password, scrambling the data. The several common methods of encryption perform differently. WEP is the weakest and most easily cracked by a hacker. Avoid it unless it's your only option. WPA provides better protection, but WPA2 is ideal for most simple networks. Add that security in the router settings, likely WPA2 Personal if your small business uses consumer hardware.

Filter by MAC address. And you can allow only known wireless clients into your network by referencing a table of unique MAC addresses. While this identifier can be faked, it's generally a single ID assigned to network-connected hardware at the factory. Connect the wireless client to the router like you normally would, and visit the router's list of clients. The MAC address should be listed there. Copy the address, and open the MAC filter list configuration page. Add each client, then activate filtering, so only devices with those known MAC addresses can connect. Remember to include mobile phones, wireless music players, or any other Wi-Fi hardware beyond laptops.