How a VPN works, and when you actually need one

A private tunnel through a public place

VPN stands for Virtual Private Network. It is an app that sends all your internet traffic through a protected tunnel to a server run by the VPN company, before it goes on to the website you want.

Imagine posting letters in a busy office. Normally, anyone handling the post can see who each letter is addressed to. With a VPN, you put every letter inside a locked bag addressed to one trusted forwarding office. People along the way just see bags going to that office. The office opens the bag and posts each letter on for you.

What happens, step by step

1. You switch on the VPN app. It connects to a VPN server, often in a country you choose.
2. From then on, your device encrypts (scrambles) everything before it leaves, so it can only be unscrambled by the VPN server.
3. The VPN server unscrambles it and sends it on to the website.
4. Replies come back the same way, through the tunnel.

Two things change. First, people on the same network, such as the cafe Wi-Fi owner, and your own internet provider, can see that you are using a VPN, but not which sites you visit. Second, the websites see the VPN server's IP address, not your home's. See What's an IP address?

What a VPN does not do

This is where adverts tend to overpromise. A VPN does not:

• Stop scams or phishing. If you type your password into a fake site, the VPN delivers it safely to the criminals. See Phishing basics.
• Protect against viruses or dodgy downloads.
• Make you anonymous to accounts you sign in to. If you are logged in to a social network or email, it still knows it is you.
• Stop cookies and tracking. Websites can still recognise your browser. See Browsers and cookies.
• Make you invisible to the VPN company. You are moving trust from your internet provider to the VPN provider, who could see where your traffic goes.

Also, most websites already use HTTPS (the padlock), which encrypts what you send to them. So a VPN adds less protection than it once did, although it still hides which sites you visit from the local network.

When a VPN is genuinely useful

Before using a VPN to appear to be in another country, check the terms of the service you are using and the local law. Some streaming services do not allow it, and some countries restrict VPN use.

Choosing a VPN sensibly

• Be cautious with free VPNs. Running servers costs money. Some free services pay for it by collecting and selling your data, or showing adverts.
• Read the privacy policy. Look for a clear statement on what is logged, and ideally an independent audit.
• Get it from the official app store or the company's own website, never from a pop-up advert.
• Ignore scare adverts claiming your phone is "infected" or "being watched" unless you install a VPN right now. That is a pressure tactic.

Tip: On public Wi-Fi without a VPN, your phone's mobile data is often the safer choice for banking or shopping.

Want the technical version? See VPNs and IPsec.