Defending your computer against intruders doesn't have to cost you a penny. June 30, 2007 The Internet is a dangerous place. Spyware, viruses and other malware (rogue software code) can corrupt your files, steal your personal data and even turn your PC into a spam-spewing zombie. Although Microsoft and other software vendors have redoubled their efforts to bolster computer security, it's still up to you to stay safe online. RELATED LINKS Laptops for Under $500 No Place Like a Home Server Whether you're running Windows XP or Vista, three security tools are essential: a firewall, anti-spyware software and anti-virus software. Although Microsoft has talked up Vista's security improvements, the new operating system is still vulnerable to attacks. In fact, Microsoft has already issued several Vista security patches -- surprising, given the system's prerelease hype. Security doesn't have to cost you a bundle. In fact, there are free choices for all three lines of defense. Or you could install a software suite, which is easier to manage than a collection of individual applications. You'll pay to install the most popular suite, but -- surprise, surprise -- there is an excellent, free alternative. Start with a firewall Both XP and Vista come with a one-way firewall that keeps hackers from invading your PC. But a one-way firewall won't stop malware already on your system from broadcasting to the Net. For that, you'll need to get a two-way firewall, which monitors both inbound and outbound traffic. For home users with one computer, a good choice is ZoneAlarm's free firewall. If you want added security for home networks, ZoneAlarm sells an advanced firewall for $40. Advertisement Disarm spyware Some spyware is annoying but relatively benign (for instance, pop-up ads that may appear on your screen). Other spy programs are downright evil, collecting sensitive personal information. The good news, penny pinchers, is that you can download an anti-spyware program and not pay a dime. Microsoft's Windows Defender is free for XP users (Vista users already have a copy). Defender is easy to configure, and it runs automatically in the background. When it detects spyware, it describes the threat and suggests a course of action. Defender is fine for most home users -- and you can't beat the price. Inoculate your machine Viruses can wreak havoc. Whether you're running Vista or XP, anti-virus software is a must. A proven winner is Symantec's Norton AntiVirus ($40), which blocks both viruses and spyware. Or you could load Norton Internet Security ($70), an all-in-one security suite that includes a two-way firewall. The suite also inspects banking, retail and investing sites to make sure that they are not fakes. Critics have slammed security suites for dragging down PC performance. But Norton Internet Security 2007 is faster than earlier versions. Advertisement And, yes, there is a free suite. AOL's Safety and Security Center provides all the protection you need, as long as you sign up for a free AOL account. One caveat: When the security console is open, you'll have to view ads in a bottom window. The ads, however, are easy to ignore. For casual users who don't regularly frequent the dark side of the Net -- which is a nice way of saying gambling, porn and other questionable sites -- a suite may be overkill. Says Richard Vamosi, CNET's senior editor and security columnist: "If you don't go to risky sites, you can probably get away with minimum protection."