Traditional virtual private networks, which are secure pipes back to the main corporate network, were designed to work with personal computers and laptops plugged into a phone or data line. But more recently, field workers have begun accessing VPNs from outside of the office or workplace, using a laptop and wireless card, or a smart phone. Meanwhile, many of the applications these employees use aren't designed for wireless networks and their less-reliable connections, and that is driving demand for software from mobile-VPN providers, whose aim is to make the connections stronger, or to keep the programs running even if the connection is temporarily severed.