I USE the Internet a great deal, but live in fear of contaminating my system with a virus that could attach itself to one of the many programs I constantly download onto my PC. I use Norton AntiVirus to scan all the programs I download after they are on my hard disk, but it would be so much more convenient to be able to scan them as they are downloaded. Is there any anti-virus software that will do this for me? MICHAEL TSOI Repulse Bay Experts agree that the growing use of the Internet has led to a corresponding rise in computer viruses. It has surprised me that no anti-virus software maker had come up with a product that will do what you want. Until now, that is. McAfee Associates, the software maker famous for its top quality virus scanning and other utility programs, has just introduced a program that does exactly this. Called WebScan, the program is said by McAfee to be able to stop users from downloading virus-infected files from the Internet or other on-line services such as CompuServe or bulletin board services (BBSs). Not only will it scan files downloaded using FTP (file transfer protocol), for example, it will also scan files attached to electronic mail for rogue macros and viruses. WebScan will work in conjunction with some of the most popular Internet navigation tools such as Netscape Navigator, Spry Mosaic and Netcom NetCruiser, among others. For more information about WebScan or other McAfee products, telephone Hong Kong software distributor SkyNet Consultants at 2520-2608. I AM a freelance writer and just started doing work on newsletters for a number of clients. I am beginning to learn about the intricacies of desktop publishing, and a few details about scanning photographs elude me. For example, if I want to use a photograph in a newsletter, how big should it be? I currently scan them in at a resolution of 300 dots per inch. Is that the best? Is it true that if I scan a photograph into my system at a greater size than I need, I will end up with better resolution? NAME AND ADDRESS SUPPLIED Let me answer your last question first. It is always best to scan in an image at exactly the right size you need. Scan it larger only if you plan to save it and think you may want to use it larger later. Scanning photographs for publishing does not, however, only involve size. When a publication gets to a printer, for example, he will tell you how many screen lines per inch should be used for your publication. The better the quality of paper, the higher the screen line count. It can be as low as 65 lines per inch all the way to 175 lines per inch. It is always best to ask your printer for the screen line count suitable for the paper you have picked for your newsletter before scanning your photographs. After you have done this, you can scan your image at a resolution (measured in pixels per inch, not dots per inch) that is 1.5 times to twice your line screen count. If you scan an image at a higher resolution than you need, you are not going to get better quality. Your system will simply discard the excess data when you prepare your publication for output. Of course, the higher the resolution of your scan, the larger the size of the file on your system. A 300-ppi image may take up as much as two megabytes, while a 170-ppi image can be only about 640 kilobytes. I have known some large high-resolution images scanned for use in top-quality glossy magazines to take as much as 50 MB of space. Keep in mind that the bigger the file, the slower your work will become. If you do not need a high resolution image, do not waste your time scanning a photograph as such and then working with it. Save yourself some disk space, too. One other tip: if you do get into some form of desktop publishing that demands the use of high-resolution images, always scan a picture as a low-resolution image and work with that through the proofing stage, switching to high-resolution for final output. You will save yourself considerable amounts of time that way. JUST a bit of extra information that might interest some readers: electronics giant Toshiba has announced that it has made a prototype of a super-density disc read-only memory (SD-ROM) drive that it believes will be the next-generation of high-density optical disc technology for computers. Toshiba said the SD-ROM drive would be compatible with existing compact discs and CD-ROMs, adding that it would also offer 'an extensive range of advanced features'. The SD-ROM, the first of its kind, would meet 'all requirements of computer makers and users for a next-generation data storage medium', Toshiba said. Send your questions to Tech Talk, Technology Post, G. P. O. Box 47, Hong Kong, or fax 2680-8167.