Use a VPN
Never assume your Mac is safe when using a shared network, whether that's out and about in a café, or even in location such as an office. Unfortunately, it's extremely easy for malicious interests to spy on data you send to and from websites.
While out and about many people chose to utilise a virtual private network (VPN) service. This encrypts all data and routes it to an end point operated by the folks who run the VPN service. Tasks such as browsing and downloading are entirely unaffected as far as the user is concerned, but anybody on the same physical network - such as another computer on the café's shared Wi-Fi service - is blocked entirely from snooping on your Mac's data.
Because a VPN service encrypts your data, you can also it at home to overcome Internet censorship imposed by the British government and ISPs.
A variety of companies offer VPN services and they're usually paid for via monthly subscription fees of around $5-$10. Just search Google and you'll find many examples. However, there's been an increasing trend recently for some companies to offer lifetime subscriptions to their VPN services for a one-off fee of around $40. For the more casual user such deals are ideal.
Typically, VPN services come with an app that you run when you want to make use of the VPN connection, although OS X/macOS comes with a built-in VPN tool that you can use instead - just open System Preferences, click the Network icon, then click the plus button at the bottom left beneath the list of connections. In the dialogue box that appears, click VPN from the dropdown list alongside Interface, then select the service type from the list beneath (usually it's L2TP). Then click the Create button, and fill-in the server/login details provided by the VPN service.
For historical reasons most data is transmitted on the web in plain form and this means anybody can eavesdrop at any stage of transit. The exception is secure connections such as those made to banks, webmail services and online shopping sites. These use secure HTTP, and you can tell because the website address starts with https://.
Wouldn't it make sense if every site used HTTPS? Making a website secure in this way is a bit more complicated and expensive than running a basic site but nonetheless there is a slow revolution happening and many sites are making the switch.
You could try adding an S to the middle of each web address - so thathttp://example.com becomeshttps://example.com. There's an https:// version of the Google home page, for example. However, an easier way if you're using a browser that isn't Safari - such as Chrome or Firefox - is to install the HTTPS Everywhere browser extension. This simply (and invisibly) consults a database of sites that have an optional https:// entrance and switches you automatically should you try to access one.
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