There is no absolute guarantee of safety or privacy. Whatever security measures can be created by humans can be subverted by humans. Paper checks can be stolen from the mail or forged, debit card number and PINs can be captured from an ATM or gasoline pump, your data can be captured through a third party network server, cash can be stolen from your pocket. A friend had his passport, all of his identification, money, credit cards, and a laptop filed with lots of very valuable proprietary information stolen by thieves who pumped sleeping gas into the Russian railroad car he was traveling in and cleaned out every passenger in the coach.
The absolute best you can hope for is to reduce the risk to an acceptable level and what is acceptable is a personal decision. The risk of logging on to WiFi networks in hotels, airports, on airlines, in coffee shops is statistically greater than logging on at your home or office, but probably not that much greater — provided you use common sense and a modicum of caution. But again it all depends on how paranoid you are and your personal comfort level.
NOTE: being a little paranoid is probably wise.
If you are seriously concerned about security for whatever reason, willing to spend some money, can accept slower data transfer rates, and can tolerate some inconvenience you can get a significant security increase by using a
VPN (Virtual Private Network). There are a number of VPN clients available through the App Store and most are available for MacOS, iOS, and many even support WatchOS. As an example
VPN Unlimited is available on all three platforms, is highly rated, and costs $5 a month ($25 a year) and a subscription covers five devices. There are free VPN services, but like most things, you get what you pay for.
