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Computer viruses (BMJ 296-013)

John Asbury
British Medical Journal, vol. 297, pp.246-247
ISSN 0959-8138
July 1988

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Some time ago an intensive care unit in Glasgow found that its normally well ordered computer network was becoming erratic: data were being corrupted and files were being lost. Recently a general practitioner who used an IBM compatible computer for his repeat prescriptions discovered that important files were being corrupted. In both cases a computer virus was at work. Eventually the viruses were identified and exterminated, but not quickly and not without the loss of data.

A computer virus is a small piece of computer code which has been maliciously inserted on computer storage media such as floppy disks to corrupt data. Like their biological equivalent computer viruses can infect other computers and their storage media, and a mechanism ofselfreplication is built into the code.

Viruses have become complex as computers have developed and become widespread in the past few years. They work in many ways. Some append themselves to the directory track of a floppy or hard disk. Others insert themselves into the battery backed random access memory in a computer and infect any disk that is inserted thereafter. All the viruses can be readily communicated by floppy disk, as the users of some Macintosh games software found a few months ago.

Viruses can spread through computer networks; whenever files are copied from a central source, such as a bulletin board, the virus may be copied as well. This happened recentlywhena virus thatdisplayed a seasonal greeting was downloaded by thousands of users of the IBM international network; within hours it had swamped the network.

Viruses can also spread when software on floppy disks is exchanged among the computer fraternity. Some viruses have been found embedded in games and only become activated when the game is used.

Not at risk. ENIAC, the first electronic computer

Not at risk. ENIAC, the first electronic computer

How do you know when you have a virus in your computer system? Unfortunately just losinga fileor a smalldegreeofdatacorruption is not diagnostic of the presence of a virus. With modern hardware, however, such events are uncommon and should prompt the user to keepa recordofthe software associated with the event and look out for further occurrences. Some ingenious viruses randomly corrupt computer data and at an extremely slow rate; thus users might have viruses in their system and be unaware of them for months. Viruses are exceedingly difficult to detect and recent specimens have shown an ability to change their code as they pass from host to host.

How can we deal with the problem of viruses? There are several computer programs designed to detect viruses or plot their paths. Unfortunately at the moment the advantage lies very much with the viruses as they can infect faster than they can be detected, and the modern ones can lie dormant within obscure parts of a computer for months before doing any damage. At the moment prevention is better than cure.

The main cause is that the computer system has received software from outside sources - for example, a floppy disk or network. So with an uninfected system the first step is to buy software from reputable sources. This is not complete protection, but at least users can hold the producers responsible if their system becomes infected and loses data.

Secondly, if a user does obtain software from other sources it is important that the software has a probationary period through several cycles of use when time specific precautions must be taken such that it cannot possibly infect other media. The software must be run only on computers that do not have other media such as hard disks, and precautions must be taken to ensure that the battery backed random access memory is fully erased so that ifa virus has been inserted it will be exterminated. In addition, a log should be kept of the use of the program so that suspect disks holding the code can be identified.

Computer viruses can and will continue to do enormous damage, and we must be aware of where they might appear next - for example, in major defence systems, credit rating agencies, or banks. There may even now be dormant viruses in large computer networks awaiting only the right moment for them to be activated - for example, the dismissal of a disgruntled employee. Currently technology is not adequate to detect viruses and therefore prevention is the only cure. -

JOHN ASBURY, senior lecturer in anaesthetics, University of Glasgow
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