Maybe you have mobile employees without fixed access, who want to come in from a variety of sites. Salespeople are the typical example, as they may need to connect to your network from a hotel room or a customer site.
Things may actually be easier for them, depending on how much trust they request from your network. In recent years, Secure Sockets Layer (SSL) VPN appliances, such as those sold by Aventail and Juniper, have sprung onto the planet, and ask nothing of the visitor except an SSL-enabled browser: No software installation, no matching hardware. Remote users can come into the VPN from anyplace that has an SSL browser or kiosk.
The administrator manages access rights and authentication rites in advance, setting up different rules based on who the user is, how secure a "neighborhood" he's calling from, and so on. If he phones into the office from an airport kiosk, the user may not see those medical records he would get if he were calling from an approved device at home -- at least not if the administrator set things up correctly. You don't want the good doctor looking at your record from the airport, because he can forget to log out. "Hey, look at this, man." "Is this thing on?" Talk about letting in the rabble.
And therein lies the first of the security concerns with SSL VPNs. Another concern with SSL VPNs is the recent discovery that local desktop search engines cache and index SSL VPN sessions, even though the VPNs have tools to wipe their own caches. Some SSL VPN vendor tools are available to combat this new threat.
Microsoft Terminal Services
Microsoft Terminal Services lets users work on applications in thin client fashion from a remote location. Terminal Services, part of Windows' NT Server 4.0 Terminal Services Edition, Windows 2000, and .NET Server, is a time-honored institution at many shops with ID badges and telecommuters who sport authentication token fobs. They get a new password number each 30 seconds and type it, along with their login, whenever they need to get in. (That's just one way to authenticate, of course.)
When initially released, "Term Server," like its parent, Citrix WinFrame, from Citrix Systems, Inc., became an enticing way for many shops to let employees access applications remotely, and it remains so to this day. With the addition of Citrix' Secure ICA Services' 128-bit, end-to-end encryption, (not included) Term Server traffic becomes more secure. You have to think about what happens after that secure log-in.
It's Not the Aliens: Remote Control
Perhaps the easiest to set up, lowest-budget solution for telecommuter access is remote control software, such as Symantec's PC Anywhere. These packages allow the remote user to literally control the machine back at the office. VNC is an open source selection that runs on Windows, Mac, Linux, and other platforms; it can be more trouble and additional skills are required, but you only pay if it works.
Some remote control software, such as Netopia's Timbuktu Version 7, use non-standard encryption when sending copies of your screen over the Internet. Currently, Timbuktu uses a proprietary method to scramble bits and randomize parts of the screen. Experts advise against using home-grown encryption, as even well-known methods often fail to pass muster once put under scrutiny and, with a proprietary cipher, you're getting what Gramma called "a pig in a poke." (Netopia says it plans to employ an as-yet unannounced form of standard encryption in its next version of Timbuktu.)
Meanwhile, Altiris Inc.'s Carbon Copy uses 128-bit MD5 encryption during authentication only, and the MD5 collision weakness that came to light in 2004 shouldn't be a problem for Carbon Copy. However, Carbon Copy's data stream is guarded by a 64-bit proprietary encryption key for each packet sent. Users may define any key for authentication of the data stream -- presumably if they provide the key.
Symantec Corporation just announced PC Anywhere 11.5 with AES encryption (up to 256-bit cipher strength) for both authentication and the data stream. The new version of pcAnywhere also offers host address blocking, 13 different methods of authentication (including RSA SecurID authentication), the ability to specify TCP/IP addresses and subnets that are allowed to connect, and the option to hide pcAnywhere hosts from TCP/IP browse lists.
Check security specs before you buy, because these things change. Go to BugTraq and check the product name (in date order) for security reports.
Also, make sure you can blank the screen in the office so telecommuters don't have an audience watching what they're doing from home.