pointed out that such bugs would often linger online. ‘Now here’s the
mystery,’ White wrote.[31] ‘Our evidence on virus incidents indicates
that, at any given time, few of the world’s systems are infected.’
Although viruses persisted for a long time in the face of control
measures, suggesting they were highly contagious, they generally
infected relatively few computers, which implied they weren’t that
good at spreading.
What was causing this apparent paradox? A couple of months
after the love bug attack, Alessandro Vespignani and fellow physicist
Romualdo Pastor-Satorras came across White’s paper. Computer
viruses didn’t seem to behave like biological epidemics, so the pair
wondered if the structure of the network might have something to do
with it. The previous year, a study had shown that there was a lot of
variation in popularity on the world wide web: most websites had
very few links, while some had a vast number.[32]
We’ve already seen that for STIs, the reproduction number of an
infection will be larger when there is a lot of variation in how many
sexual partners people have. An infection that would fade away if
everyone behaved identically can persist if some people have a lot
more partners than others. Vespignani and Pastor-Satorras realised
that something even more extreme can happen with computer
networks.[33] Because there is huge variability in the number of
links, even seemingly weak infections can survive. The reason is that
in this kind of network, a computer is never more than a few steps
from a highly connected hub, which can spread the infection widely
in a superspreading event. It’s an exaggerated form of the problem
that banks faced in 2008, with a few major hubs able to drive the
entire outbreak.
When outbreaks are driven by superspreading events, it makes
the transmission process extremely fragile. Unless an infection hits a
major hub, it probably won’t go very far. Yet superspreading can also
make an outbreak more unpredictable. Although most outbreaks
won’t take off, those that do can stutter along for a surprisingly long
time. This explains why a handful of computer viruses and worms
have continued to spread, despite not being that transmissible at an