With the advent of the inexpensive and powerful personal computer, networks have evolved and are now implemented exclusively using small computers connected among themselves and to the Internet. Don't get me wrong, though -- the mainframe isn't dead yet. In fact, Gartner estimates that more than 80 percent of business applications are written in Cobol, one of the earliest high-level programming languages. But the truth is that, although still alive and kicking, the mainframe has nevertheless lost ground in our current environment, which is focused on PCs and distributed server architectures.

Today, computer security presents a far greater challenge than it did in those early days. In the purely mainframe era -- or even in earlier days of network computing -- there were no widespread viruses or spyware to deal with, and security wasn't nearly as complicated as it is now. That is primarily because the Internet hadn't been factored into the computing equation. Sure, there was the infamous Morris worm launched way back in 1988, but that pales in comparison with what today's script kiddies can conjure up and distribute on our modern, densely populated information superhighway. The sad fact is that the Internet is rife with malware and spyware and hackers, and they are headaches that network administrators will have to deal with on a regular basis for the foreseeable future.

As if that onerous task wasn't enough, today's systems administrators often have to do their jobs while managing several different operating systems. Windows -- still the most popular operating system worldwide -- might start to lose a little more ground to Apple's Mac OS X and various incarnations of Linux simply because those systems aren't targeted by the bad guys as often as Windows and are therefore perceived as safer. Because those systems are less of a target, some network administrators have believed that their Mac and Linux boxes can be run without antivirus software. Bad mistake. Viruses such as "Virus.Linux.Bi.a/Virus.Win32.Bi.a," which appeared in April, prove that it's possible to create viruses capable of infecting both Windows and Linux.

I have little doubt that we'll continue to see increasing interest among the malicious fraternity of virus writers in creating more cross-platform malware and attacks. Therefore, when it comes to the heterogeneous computing environment, you'll need to have virus protection on all your machines -- even those that haven't been targeted as often in the past.

Unfortunately, while the number of antivirus choices available for Windows is astounding, the selection for Macs and Linux is sadly lacking. There are versions of the Clam AntiVirus freeware for Linux, Mac and Windows systems. For a mixed Linux, Mac and Windows environment, you can get products from Sophos (which I use on my Mac), McAfee and Symantec that also cover all three. For mixed Windows and Linux environments, there is also Kaspersky Lab, F-Prot, Panda and Grisoft, to name just a few. Some of these are even offered as freeware, which means there's no excuse for running bare.