St. Petersburg Times Online
 Devil Rays Forums

printer version

Caution can help secure your cable modem

The constant link created by a cable modem can leave your computer vulnerable. Here are some steps to protect it.


© St. Petersburg Times, published December 6, 1999

For those concerned about someone hacking into your computer because you use a cable modem for Internet access, here's a simple solution: Unplug the modem.

That leaves you safe, but it's a bummer if you enjoy the speed and convenience of using cable to surf the Web.

If cable access has an Achilles heel, it's security. It's not like using a phone line to get to the Web; it's more like a highway you're sharing with your neighbors. You wouldn't want someone to walk into your house and shuffle through your private papers or take a peek at confidential company information you take home. A cable modem can be like leaving your front door open when you're not home, inviting trouble.

People who connect by a phone through dial-up service are not immune, but there's a difference. Computers talk to each other on the Internet using a series of numbers called Internet protocol. Dial-up numbers change each time someone connects, offering a bit of security, though not total protection. Many cable modem users stay on the Net constantly and have fixed addresses, making them a more inviting target.

Unless you take precautions, you're vulnerable to an attack that can range from a minor nuisance to loss of data. (As reported in Tech Times over the summer, a California man using a cable modem had all his files erased by a hacker.) The problem can be caused by your cable modem service provider not securing its networks or by an insecure PC in your home. It's not just Windows-based PCs that are at risk; Macs aren't immune either.

Cable's doorway to your computer is through an Ethernet network card, a technology invented in the '70s that allows computers and other devices to hook into a local area network, or LAN.

When you connect to the Internet with a cable modem, you are joining a LAN that usually extends through your neighborhood. Most networks permit files and printers to be shared among computers on the system, and on Windows it's through a system called Network Neighborhood.

If such file sharing is enabled, anyone who knows your Internet protocol numbers can scan your hard drive. And you wouldn't necessarily know it was happening. Even if you don't have file sharing turned on, you could be vulnerable to attacks that could lock up your machine.

The Tampa Bay area's providers of cable modem service, GTE WorldWind ( and Time Warner Road Runner (, say they make new users aware of security issues.

"We do instruct that they should turn off their file sharing," said Rob Kietzman, WorldWind's director of product marketing in Dallas. "We do want to make them aware of it."

Mark Bailey, vice president of Time Warner's Road Runner Online Services in the bay area, said its installation checklist includes file and printer sharing. "If the PC does not have those enabled, we don't have that discussion," Bailey said. "If they do have sharing enabled, we let (customers) know the capabilities and the security issues at hand."

Neither Kietzman nor Bailey was aware of instances in which home users had been hacked, but both said their companies are working on security issues. (Time Warner's help desk in the bay area supports both Windows and Macintosh; GTE offers only Windows support.)

We're in the early days of cable modems, and there is an effort under way called DOCSIS that includes specifications to make the networks more secure.

You can take some simple steps to offer some basic protection to your machine. First, make sure file sharing and printer sharing are turned off.

With Windows 95 and 98, you have to turn both of these services on. If you're the only person who has used your computer and you installed Windows yourself, it's likely that they are off. (To check, right-click the Network Neighborhood icon, then click on Properties and File and Print sharing. If the boxes next to the file access and print sharing are blank, then it is turned off. If the boxes are checked, click to turn them off.)

Keep in mind, though, that if you're using a program such as pcAnywhere (, which allows you to access your home computer from another PC, and set it up with weak passwords, turning off file sharing won't do much good.

Windows NT-based PCs are the opposite and have file sharing turned on by default. It's simple to disable. However, if you are running NT, there's probably a reason for it that involves your corporate network. Check with the people you usually call for help before disabling this.

To disable file sharing in NT version 4, go into Control Panel, double-click on Services and locate the Server service. Click on the Stop button and, if you're asked, agree to stop any other services on which this depends. Now click on the Start-up button and set the start-up options to Disabled.

Even after taking these basic precautions, you could be vulnerable to attacks that could lock up your machine. Until the cable networks start protecting your machine by default, you really need a firewall, sometimes called a packet filter. A firewall acts as a network sentry, protecting your machine and advising you of misuse.

Firewalls can be software or hardware. Software solutions sell for as little as $40, which is cheap protection. A good place to start looking for recommendations is I've heard colleagues say good things about Windows-only Black Ice (, but I haven't tried it.

Each firewall package takes a different view in its approach to security, so check the specifications and talk to people who use software to get an idea of what you want to try. When you find one you like, it's a good idea to see if there's a free trial available. You can test the technical support, as well as learn what the firewall is doing and how it's protecting you.

After a lot of research, I chose a hardware solution for my home office. I settled on the $400 Ramp Networks WebRamp 700s (, which has several features: It sends me e-mail when it detects intrusion attempts, it has specific protection against well-known attacks, and it notifies me when new versions of its software are available. It allows up to five PCs to sit behind the firewall and share the static IP address assigned to me by WorldWind. Check with cable operators to see if they support this system.

If the price and the "you're on your own" feeling doesn't put you off, it's a perfect solution for high-end geeks or small businesses. Had I more time than money, I would have forsaken WebRamp, broken out the thick Unix books and used OpenBSD (, one of the most secure operating systems around.

There is a free solution that could turn an old 486 into a perfectly serviceable firewall, but it's not for the faint of heart. You'll have to have an understanding of networking basics.

If you're not frightened off, fire up your browser and head over to the Linux Router Project ( It's a skinny version of Linux, a free operating system that tastes a lot like Unix. This version is so skinny that your 486 machine doesn't need a hard disk because it will run from a floppy.

Cable modems are an exceptionally good value for the money. With a little caution and preparation, your would-be machine cracker will move on to softer targets.

-- Times Technology Editor Dave Gussow contributed to this report, which includes information from Times files.

Back to Tech Times

Back to Top
© St. Petersburg Times. All rights reserved.