When businesses send private information across the net, they place a high value on it getting to its destination intact and without being intercepted by someone other than the intended recipient. Individuals sending private communications obviously desire secure communications. Finally, connecting a system to a network can open the system itself up to attacks. If a system is compromised, the risk of data loss is high. Currently, there are no systems in wide use that will keep data secure as it transits a public network.
Several methods are available to encrypt traffic between a few coordinated sites.
Unfortunately, none of the current solutions scale particularly well. In a nutshell, IP traffic is sent across various forms of physical networks. Each system that connects to the physical network implements a standard for sending IP messages across that link. There are a number of ways to accomplish this which tradeoff between abstraction and efficiency. The advantage this gives you in terms of secure data transfer is only a single step further away.