I wrote a virus 10 years ago, but before I am dragged into Victoria Park and stoned, I would like to explain. About 12 years ago, most users had Apple II+ and MS-DOS machines. DOS had severe restrictions, but it could be made to look as if it could multi-task by writing a program called terminate and stay ready (TSR). Programming skills needed for this were considerable, and anyone trying anything exciting was attracted to writing TSRs. The most famous was SideKick, the TSR that gave you a notebook, calendar and calculator at the press of a few keys. To work, TSRs take complete control of the keyboard and most low-level functions. As a test, I wrote a program that took control of the keyboard, the clock and the screen. If you did not type anything for 10 minutes, a spider would crawl down the screen and eat everything on it. It disappeared once you rebooted. Despite the name - virus, Trojan horse or worm - files that attack systems are nothing but executable programs or macros. It is quite impossible to get a virus if you do not 'run' it. It is possible, of course, that you could run one without realising it. Using Netscape, you can access a site on the Internet that claims to need a plug-in or some other executable file. Netscape will ask if you want to save it or run it. If you trust the site, you usually run it. According to PC-cillin, there are at least 6,000 viruses for the PC. There is, of course, an inherent problem with testing this kind of software. If you have not got a virus, how do you know the software is working? Do you go out and purposely infect your machine so that you can test the product? What do you do if it does not work? I have no intention of infecting my machine with a virus, so I can only comment on certain aspects of PC-cillin. I hope, however, that users will be prepared before being infected. Waiting until you are infected is not a very smart idea. If there are 6,000 viruses out there, the cures number considerably less. Most protection software works in the same way. It scans disks or folders for 'known' viruses and scans files downloaded from the Internet, an important aspect of any program. A few years ago, viruses were spread mainly through the exchange of floppy disks; today you are far more likely to get hit from a file downloaded from the Internet. Users should be extremely aware of pirated software available from sites on the Internet: many of them will be sending you more than you bargained for. In the days when Microsoft's DOS ruled the world, F-Prot was king of the clinic. It still exists, but is losing ground to Symantec, McAfee and PC-cillin. The manager of a group of Hong Kong programmers said: 'F-Prot used to be absolutely superb. It used to be the best.' He now uses McAfee because of its 'Hunter' engine that searches out viruses. McAfee also has monthly updates on its Internet site ( www.mcafee.com ). Some reports on the Internet give McAfee 100 per cent success in its ability to find and destroy viruses. PC-cillin also has been given good marks from the Internet. It has updates on its Web page, which is an important aspect of any protection program. With Microsoft adding programming abilities to its Office Suite - Visual Basic and ActiveX - it opens up enormous scope for the user and a terrific opportunity for the virus creator. Viruses today can do serious damage to a system. The more networking we do - including the Internet - the more susceptible we are to attack. Practising 'safe computing' is the first thing, getting a virus protection program to scan incoming files is another.