Jack a computer into the Net, and your self-preservation instinct soon turns you into the Dutch lad with his thumb in the dike. But once you begin fighting sewage that includes hackers, viruses, and spyware, you quickly run out of enough fingers, toes, and chewing gum to stem the tide. Let your guard down, and the trickle can turn into a flood.

The more time I spend keeping out intruders, the more I think of myself as the maintenance manager of a virtual dam called the Antinet--a structure that may look impervious but still has major holes. I've got ZoneAlarm Pro to protect against inbound intruders, outbound Trojan horses, and pop-ups. Norton AntiVirus fights infections. The shareware Spybot Search & Destroy finds and removes spyware designed to invade my privacy or commit worse deeds. A version of SpamAssassin running on my Web host's server whacks time-sucking junk mail.

WEP encryption runs on my Wi-Fi network to keep out miscreants, even though I know WEP is a system made from bars of strongest marshmallow. I install Microsoft's endless security patches regularly, despite knowing that they sometimes make matters worse. I limit Windows file sharing to a single directory on my hard drive. And I create different passwords for the various Web sites I visit.

But despite all my precautions, sewage trickles in and essential fluids get dammed out. ZoneAlarm Pro crashes every couple of days when it runs into a Web page it doesn't like, and setting its pop-up and cookie blockers too aggressively makes some pages unusable. SpamAssassin blocks nearly 100 messages a day, but one or two are invariably things I need to read, and some junk still sneaks through. Only in the forthcoming Outlook 2003 does Microsoft begin to address the security problems in its preview pane.

And then there's the virus that mysteriously reappears on my PC every two months or so and sends itself to people in my address book. If those lucky duckies are running Norton AntiVirus, the program recognizes the virus as W32.Magistr.39921@mm and sends it packing from their systems. But neither Norton nor any other product I've tried can find it on my hard drive, let alone neutralize it--and I don't know how ZoneAlarm could have let it pass in the first place.

Imperfect software isn't the only reason the Antinet is so leaky. Tell a site that you've forgotten your password, and the chances are good you'll receive it in an unencrypted e-mail message that any snoop could intercept. Instead, you should get a link to a secure page that challenges you for additional information. That's just one example of bad Web security that can bite you no matter how vigilant you are.

The sands keep shifting, and the leaks keep changing. Conventional wisdom once had it that NAT routers, which assign private Internet addresses to machines in a local network, effectively insulated those PCs from outside attack. Now Wi-Fi gateways routinely hand out those local addresses, letting attackers vault past the firewall into what Microsoft used to call the "Network Neighborhood."

Even if we start tossing spammers and hackers in the pokey, the need for the Antinet won't disappear anytime soon. Which is why the battle cry of the Internet user is reduced to a single word, endlessly repeated: Dam!

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