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Snoops, spies, and cyberpunks are just three reasons to protect your PC with a firewall. For personal, single-PC use, a free firewall such as Zone Labs' ZoneAlarm 2.1 ($20 for business use; downloadable from FileWorld) is an effective way to shield yourself from cyberattacks.

Now, with Zone Labs' newest firewall, ZoneAlarm Pro, the company has added additional network protection to its already strong product.

Adding a layer of granularity you won't find in the personal version, ZoneAlarm Pro lets advanced users tweak specific settings, such as the security level, giving them more control over how the product works. I tested a shipping version of the new ZoneAlarm Pro ($40 for a single license with volume discounts available).

The Pro version offers the same protection against Internet hackers and viruses as the free personal version of ZoneAlarm does, but adds e-mail and security tools, along with a few other extras.

Though it sheds the personal version's flashy orange color on its interface for a more businesslike gray, ZoneAlarm Pro's look bears a striking similarity to the personal edition. Both versions are fairly intuitive and straightforward, though Pro offers advanced tools (for example, you can decide which applications access the Internet and which ports they can use).

Securing the Wall

Like the personal product, ZoneAlarm Pro features a main control panel with five buttons--Alerts, Lock, Security, Programs, and Configure--that all trigger drop-down panels where you can set preferences. For example, under Alerts you can suppress the cryptic pop-up windows and ask ZoneAlarm to record warnings in an activity log instead. Unfortunately, it's difficult to tell which area you are configuring since the buttons don't change their appearance when you click on them.

By far the biggest difference between the two versions is in the Security area. Both have the same basic sliders that allow you to choose High, Medium, and Low firewall security levels for local network and Internet zones. Beyond those three basic security settings, the new version includes a Customize button that lets you check off specific firewall rules. The choices, such as "Allow outgoing DHCP (UDP port 67)" and "Allow incoming IGMP," may look like gobbledygook to novices, but they offer valuable control for technophiles and networking professionals.

Set your Local zone to Medium security to enable file and printer sharing on your local network, for example, but block sharing in your Internet zone, where sharing can provide an open door for hackers to snoop around your hard drive. (For more about hackers and security, see "Unsafe at High Speed.") You can include trusted remote machines in your Local zone so that you can, for instance, share files between your home and office PCs.

Both ZoneAlarm Pro and the personal edition display a busybody stream of pop-up alert windows that are difficult to decipher. I was confounded when a cryptic message popped up on the screen and said, "The firewall has blocked Internet access to 209.1.108.12 (NetBIOS Session) from your computer [TCP Flags: S]."

The personal version of ZoneAlarm is targeted at home users who typically use stand-alone PCs and don't use the local network zone setting. The Pro version, however, extends its protection to networked environments, and the new Security Panel reflects that with an Advanced settings button to specify IP address sharing.