It's possible that a malicious hacker on the Internet could gain access to your computer when you're connected. In general, it's unlikely that a personal computer on a dial-up connection would be a target for a hacker simply because the connection is transient. We block the TCP and UDP ports that are known to be used maliciously, and we recommend that you install some kind of personal firewall on your PC if you are spending more than about 20 hours a month online.

ZoneAlarm is one of the best personal firewalls available, and has the added benefit of being free! We used to recommend BlackICE Defender, but recent work by Steve Gibson (www.grc.com) has convinced us that it's not terribly good.

If you must buy a personal firewall, upgrade to the Pro version of Zone Alarm. Norton Internet Security Suite also has a pretty good personal firewall.