Installing virus protection software and keeping it up to date are basic steps to shielding computers connected to the Internet.
The virus protection software manufacturers provide frequent updates on their Web sites and respond quickly to reports of new viruses.
The next level of security is a firewall, which is a software program or a hardware-software combination that stands guard between an Internet connection and computers.
Firewalls are considered standard equipment for computer networks with Internet access.
People looking to break into computers use special programs to scan Internet addresses, looking for vulnerable systems. Since many businesses with networks maintain constant Internet access through ISDN or DSL connections, a network without a firewall is like an unlocked safe.
"There's different levels of firewall protection and we tailor the installation to each client's needs," said Jeff Obst, president of edurus, a Carson City Internet provider.
Besides commercial software firewalls, some network routers have firewall protection built in and some firewalls are stand-alone hardware devices.
"We use network address translation firewalls, which prevent any requests from the outside from getting into the system because they don't know the real addresses of your computers," Obst said. "The only way something gets past the firewall is when a computer on the inside requests it."
Pyramid Net owner Bob McDermand said how a network's firewall is designed depends on the nature of the information being protected.
"Most individuals and small businesses don't have anything hackers want. They're going after the name sites," he said. "But I prefer hardware over software when it comes to firewalls. There are some new, inexpensive hardware boxes being tried by some of our customers."
Home computer users are the next target of Internet service providers who want to increase their incomes by providing high-speed, round-the-clock access, instead of the home user having to dial in for each Internet session.
But that will mean the home computer has a constant Internet address, instead of one that changes with each dial-in. And the computer may be on for hours, increasing its vulnerability.
"Cable modems are a big problem. Someone in your neighborhood might just as well be in your hard drive," McDermand said.
Obst said the anticipated boom in DSL and cable service may induce hackers to probe home and small-business computers.
"Fast connections that are on all the time - that's what attackers like to go for so they can do their thing at 2 a.m. or whenever."
He said firewall software is beginning to come on the market for the individual computer user and may become as standard as virus protection.