So, first of all, I would like to conclude.
"You can only use your browser while using free Wi-Fi, and only access sites that start with'https'."
Whether you're a person who doesn't really understand what you call security, or with the help of others, please be aware of this. I think "Safari" for iPhone and "Chrome" for Android are the mainstream browsers, but use only those two while connected to free Wi-Fi, and refrain from using other apps. Then, from that browser, only access sites with URLs that start with "https". This at least reduces the chances of someone stealing your information (although if you already have spyware, that's a different story).
Example of https display. This is the Android version of "Chrome" where I opened the Google website. In addition to the padlock icon, the letters https are green. The introduction of https is quite widespread, but not yet complete.For example, DMM keeps http on normal pages, but uses https only on some pages such as shopping cart screens.In communication by https (SSL / TLS), the communication between the server and the smartphone is encrypted at a different layer from Wi-Fi. I don't know what will happen depending on the progress of technology in the future, but at least at this stage, you can trust the high confidentiality of https communication.
However, what about applications other than browsers ... for example, communication performed by SNS clients and games? Communication should be encrypted if you think in common sense, such as an application that exchanges messages or a login screen of a game application, but there is no way to explicitly know whether it is https like a browser. Perhaps you are sending and receiving in plain text without encrypting your registered email address or ID. Or the in-game chat may be missing.
That's exactly why I explained, "Use only the browser."
That said, it's tough to keep this 100%. There are many things I want to do, such as posting photos taken on the go with an SNS app or using free Wi-Fi. What should I do as a matter of fact?