VPNs are resource-intensive and can take a huge toll on your network bandwidth, which is why you should only employ them when you need them.

A virtual private network (VPN) can be an important tool in your online protection routine, but only if you know exactly what a VPN can and can't do. Used properly, a VPN can enhance your security and privacy, especially when traveling, but it's not a replacement for other tools. For further information, check out our guide on what is a VPN. 

Also: Public Wi-Fi safety tips you need to know   

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The basic concept behind a VPN is simple: software running on your PC encrypts every bit of network traffic before it reaches your PC's network adapter, then it sends that encrypted data to a remote server that's operated by the VPN service. That remote server sends the data to the public internet. The encrypted "tunnel" between your device and the VPN server is what makes the network both virtual and private. Many corporate networks will only allow remote connections over a VPN. Still, you can also buy consumer-grade VPN software for connecting to untrusted networks, such as those found in airports and coffee shops.

The benefit of this type of network is twofold. First, it prevents anyone on your local network from spying on your internet traffic. That's especially important if you're using a Wi-Fi network that's not under your control. 

Second, it allows you to disguise your location, which prevents some types of tracking and also makes it possible to bypass geographic restrictions on some services. If you're in Europe and want to watch a movie that's restricted to the US, you might be able to fool the streaming service by connecting to a VPN in the US.

Even the best VPNs are resource-intensive and can take a huge toll on your network bandwidth, which is why you should only employ them when you need them.

Also:Is there a good free VPN? Well, you get what you pay for

When I'm in an airport or hotel, I prefer to tether my mobile phone to my laptop (or bring a device with a built-in cellular connection) to avoid the risks that come with that untrusted network. But if the cellular signal is weak or unavailable and I have no other choice than to connect to that public Wi-Fi, I use the paidFastVPN service from NameCheap. My colleague Jason Perlow usesExpressVPN . 

"It's compatible with OpenVPN, an open source VPN protocol," he says, "which means I can use it with all the devices I own -- iOS, Android, Windows, even on my network firewall." 

Regardless of which option you choose, nothing in that virtual private network looks for threats to your PC. If you download a piece of malicious software or visit a website that contains a drive-by exploit, the fact that your network is private is irrelevant. The same is true if you or someone in your home or office gets taken in by a phishing email. Typing your credentials into a bogus website generally leads to bad outcomes, and a VPN won't magically protect you from that sort of error.

For effective protection against malware, you need security software that's specifically designed to sniff out malicious software, regardless of how it's delivered.