If you’re using public Wi-Fi, anyone with the password and a little tech know-how can eavesdrop on your online activity. VPNs, or virtual private networks, come in handy by masking your online activity and location, and routing the data you send and receive through a secure virtual tunnel between your computer and the VPN server.

Here’s how an internet connection works without a VPN. When you type a website address into a browser, your ISP taps into your router — that device in your living room with an impossible-to-remember password — to forward your internet traffic to that website. Your ISP also assigns a unique number, called an Internet Protocol (IP) address, to the router, and each computer or phone connected to that router. Some websites, ad networks, and platforms — such as Google, for example — use your IP address to track your location information for marketing purposes.

Although VPNs keep prying eyes off your information from the outside, some question the VPNs themselves. After all, can’t they simply track your information? Here’s how to make sure you choose a safe VPN.

A no-log VPN means the network doesn’t collect, or “log,” any information transmitted through the network. It doesn’t save your personal details, where you go online, what you download, or your search history. This ensures your online privacy and anonymity are protected from everybody — even your VPN provider. So, if a cybercriminal does happen to penetrate a no-log VPN, there won’t be much to find.

How secure is a VPN? VPNs secure your public internet connection by encrypting your information and shielding your online activity from cybercriminals and even your own Internet Service Provider, or ISP. In terms of your online privacy, the most secure VPNs are also likely transparent about their privacy policies, take steps to fix leaks, and won’t keep logs of your browsing history.

When you use VPN software, your device connects to the VPN provider’s servers. Your internet traffic passes through the VPN’s internet connection, meaning your private information is cloaked from your ISP and websites so they can’t log your web browsing. As the VPN server mixes your web traffic with others on the server, your IP address appears to match the one associated with the VPN. These steps make it harder for others to monitor and gather information about where you go and what you do online.