In many cases, each of these offices also have LANs. But how do the LANs connect? For some very specialized solutions, companies lease private lines to connect the offices. That can be very expensive. Instead, most companies opt to geographically connect separated private LANs over the public internet. To protect their data, they set up VPNs between offices, encrypting the data as it traverses the public internet.
Whether the VPNs you’re familiar with are the ones offered by your school or business to help you work or stay connected when you’re traveling or the ones you pay to get you watch your favorite shows in another country as they air, they’re all doing the same thing. For much more detail on what VPNs are, how they work, and how they’re used, check out this How Stuff Works article.
There was a time when using a VPN required users to know about the built-in VPN client for Windows or universal open-source solutions such as OpenVPN. Nowadays, however, nearly every VPN provider has its own one-click client that gets you up and running in seconds. There are usually mobile apps as well to keep your Android or iOS device secure over public Wi-Fi.
That attitude to the safety and privacy of personal data creates an enormous online security risk. Public Wi-Fi networks, which are ubiquitous and convenient, are unfortunately also highly convenient for attackers looking to compromise your personal information. How do you know, for example, that "starbucks_wifi_real" is actually the Wi-Fi network for the coffee shop? Anyone could have created that network, and they may have done so in order to lure victims into disclosing personal information over it. In fact, a popular security researcher prank is to create a network with the same name as a free, popular service and see how many devices will automatically connect because it appears safe.