RIDDING your computer of a virus does not mean you can relax. It could return
months or even years later鈥攁nd researchers will tell a conference in Paris
next week that this is much more likely to happen than was previously thought.
What鈥檚 more, things can only get worse as the Internet expands.
Until now, most analysis of the way computer viruses proliferate has been
based on some of the ways biological viruses spread. Numbers of the virus either
increase exponentially, with each computer infecting several others in a chain
reaction, or it dies out quickly. Which of these paths is followed depends on
whether a virus infects new victims faster or slower than it is purged by
anti-virus software.
But physicists Romualdo Pastor-Satorras and Alessandro Vespignani at the
Abdus Salam Centre in Trieste, Italy, now say this model doesn鈥檛 reflect
reality. The pair examined 814 persistent computer viruses reported in Virus
Bulletin from 1996 to 2000. They found that none of the viruses spread
exponentially. And contrary to expectations, viruses with very low infectivity
rates stayed around for many months
(see Graph). So Vespignani and
Pastor-Satorras, now at the University of Barcelona, have devised a new model of
virus epidemiology which takes into account the fact that the number of
connections between computers on the Internet fluctuates wildly (New
快猫短视频, 29 July, p 4).
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鈥淚t means sometimes an infective virus will die out because it doesn鈥檛
encounter enough connections, whereas a less infective one might spread,鈥� says
Vespignani. He says safety measures which affect the connectedness of the
network鈥攕uch as telling people not to open e-mail attachments鈥攁re
more important than the distribution of specific anti-virus software.
However, Graham Cluley of the anti-virus company Sophos, based near Oxford,
says the problem is that not enough people employ the anti-virus software that
is available鈥攁nd don鈥檛 apply important software 鈥減atches鈥� that keep
viruses out. But according to Vespignani, unless almost everyone uses anti-virus
software, a virus can become endemic.