If Windows knows it's accessing a public network, it will hide your laptop from other computers and devices. That provides significant, but not perfect, protection. So you have to make sure Windows knows you're on a public network, and you need to take additional precautions.
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When Windows logs onto a Wi-Fi network that it doesn't recognize, it will ask you how it should handle security. And if for some reason it doesn't ask, you can manually make it bring up the question itself.
How it does this depends on your version of Windows.
Windows 7
When you log onto a new network, Windows 7 brings up a large dialog box where you can declare whether it's a Home, Work, or Public network.
If the dialog box doesn't come up, or you're not sure you gave the right answer, you should confirm that Windows knows it's a public network. Go to the Start menu's Search field, type network and, and select Network and Sharing Center.
Once there, you'll see the name of the network, and below that, the network type. The type is a link. Click that link, and you'll get to the same dialog box that was supposed to come up automatically.
Windows 8
When you log onto a new network, a panel will appear on the right side of the screen, asking if you want to find "PCs, devices, and content on this network." If it's a public network, select No.
If you want to make sure the setting is correct, go to the Search charm, type network, and select Network connection settings. Select your network. If the Find devices and content switch is turned off, Windows knows it's a public network. If that switch is on, turn it off.
Other precautions
In theory, that should be enough. But it's wise to take additional precautions:
That should keep you acceptably safe.