As the name implies, a VPN is a network that is virtual. That is to say, unlike the local network at a business or small office that consists of, in some cases, many thousands of yards of cabling and many network devices, a virtual network contains no substance at all—in fact, it exists on top of existing networks. It is also private, which means in this case that it is both encrypted (so that third parties cannot see what we are sending and receiving) and authenticated (we need to identify ourselves, generally with a password, in order to use it).

Consider a scenario involving a small company with a small number of sales employees who routinely work from different parts of the country (or even the world). The sales staff needs to regularly synchronize its sales information with the other sales employees, both out of the office and in the office, and it needs to send and receive email and access other types of company information. These services have, until now, been accessible...