PJML@ibma.nerc-wallingford.ac.uk (Pete Lucas) (01/03/90)
The 'biological' analogy of a computer virus provides a useful model for computer viruses: As a biologist who computes (rather than a computer person) there are various things to consider:: 1) Disease vector - diskettes, networks, cartridges, WORM disks etc. 2) Incubation period - how long between initial 'infection' and the symptoms becoming noticeable. 3) Latency period - how long between infection and the infected machine becomin g able to pass on the infection to another machine. 4) Contagion - how rapidly does the virus spread once it has become activated 5) Damage - what is the severity of infection once it has been activated. 6) Reservoir of infection - the diskettes locked away in your drawer for six months, that you 'thought' were clean!! In biological terms, a 'successful' parasite (since that is what a virus is) can adopt several strategies. It can be highly infective (so it gets spread to many new hosts) but have a long latency period (so the host shows no symptoms until it has been infected for a long time), or it can be of low infectiveness with a short latency (so if you catch it, you suffer immediately, but the chance of you catching it in the first place is low anyway). Similarly, the harmfulness can vary. Any parasite that is immediately fatal to its host is going to get noticed, but if it has been able to pass on the infection before it 'kills' the host, it will survive - similarly if the virus remains infective after the host has died, it may still spread. Computer-viruses we have seen so far tend either to be massively infective, or have long latencies, or both. This leads them to be noticed, and people write anti-virus software to combat them. A virus that has a very long latency and low infectivity (so it spreads slowly, unnoticed and unexpected because nothing untoward is happening) but has a high damage-causing ability when triggered, is probably the worst thing to contemplate, since it could become established in a large population of machines unnoticed, then trash the lot. I am thinking here of something with a latency of years - what about a virus that triggers only on February 29th? The virus that remains infective even after the 'death' of the host is with us - your PC may have been crashed, but your diskettes may also be infected and spread the infection to other machines even though you have 'disinfected' the originally infected machine. Diskettes will always act as a reservoir to re-infect otherwise 'clean' machines. Pete Lucas PJML@UK.AC.NWL.IA