Frankfurt - Wi-Fi Hotspots - zones that offer free wireless internet connections - are almost impossible to avoid these days in larger cities, popping up in cafés, airports and train stations.But just because the internet connection is freely available doesn't mean users shouldn't take some precautions to protect their personal data."Every time I use Wi-Fi, I have to ask myself who's behind it," said Frank Timmermann of the Institute for Internet Security at Germany's Westphalian University of Applied Sciences."That's because I'm just connecting myself with an access point that uses a given name and a Mac address."The problem with that relative simplicity is that any router owner can pick any name for his network. A network that sounds like it's run by a city authority might just be a private one. And that someone could be a person capturing data traffic for his own ends.Encrypted connectionsThat risk is one good reason to only send information with encrypted connections, which can be recognised by a web address that begins with "https" and had an icon of a padlock in the address bar.But that's not always an option. Apps don't offer this kind of security. "With those, I don't know if I'm communicating with encryption."The same problems can pop up in one's home network, he added. While data on a public network can be snatched before it reaches the router, any information sent to any router - even one's own - can't have its safety guaranteed once the router sends it on."I don't know what comes after the router, who's sitting on the line," said Timmermann.Another problem with a public Wi-Fi network is that other users can take advantage of it to attack other computers. That means leaving drives and files unprotected - which is convenient when working in one's home network - should not be an option when out and about."Your computer should be set up for basic protection anyway," Timmermann said. That means a virus scanner and a firewall, as well as up-to-date software.Also check the terms of any open network you use. Some are only free for a certain time, others are only accessible once users give up personal information. That can be risky, said Timmermann."If I first have to provide my e-mail address to get into an open Wi-Fi network, then I'm easier to identify," he said. "And a potential attacker will always be happy if I just give up personal information that way."