This is excerpted from a New York Times article.
“That free Wi-Fi network may not be so free if it is unsecured and someone hijacks your data. Your phone’s cellular data connection offers more protection.
If you are unfamiliar with the available wireless network nearby and want to be as safe as possible, stick with the LTE data connection. If your data plan is limited or you need more speed than what the cellular network offers, use a virtual private network like F-Secure’s Freedome VPN or Private Internet Access to encrypt your Wi-Fi connection.”