EVOLUTION
EVOLUTION BEGANS
Just
as external factors such as drought, sanitation and migration have a strong
influence on biological epidemics, changes in the computing environment are
responsible for the presence of several distinct epochs in viral infection.
Until 1992, reported sightings of file-infecting viruses and boot viruses
occurred at roughly equal (and steadily rising) rates. Then the incidence
rate for file infectors began to fall dramatically, whereas that for boot-sector
infectors continued to rise. Between late 1992 and late 1995, boot-sector
infectors reigned supreme. Why did the file infectors essentially become extinct?
REASONS FOR WIDESPREAD OF VIRUS
We
believe the cause was the widespread acceptance of Windows 3.1, an enhancement
to MS-DOS--the operating system used on most computers--that became popular
around 1992. Windows crashes readily in the presence of typical file viruses,
and so necessity will lead afflicted users somehow to eliminate the virus
from their systems (perhaps by wiping out the hard disk and reinstalling all
the software), regardless of whether they know that the symptoms are caused
by a virus. Boot viruses, in contrast, tend to coexist peacefully with Windows
3.1; they do not kill their hosts before the infection has a chance to run
riot.
HOW WE AID VIRUS IN THEIR EVOLUTION
The
wide use of Windows 95, yet another new operating system, has now led to a
precipitous decline in the prevalence of boot viruses. Windows 95 warns the
user about most changes to boot sectors, including many of those caused by
viruses, and most boot viruses cannot spread under Windows 95. We have already
seen a handful of viruses specifically designed for Windows 95 and other 32-bit
operating systems, although the ones we have seen are unlikely to become widespread.
MACRO VIRUS....A NEW THREAT
We
are now in the era of the macro virus. Because users tend to exchange documents
and other data files capable of harboring macro viruses more frequently than
they exchange programs, macro viruses enjoy a higher birth rate and thus spread
faster than the traditional boot or file infectors. Sophisticated mail and
file-transfer functions now permit users to share documents or programs more
quickly and easily than before, exacerbating the problem.
THE NEW DANGER
Macro
viruses are also the first viruses to exploit the growing trend for interoperability
among computers. A DOS file infector can never endanger a Macintosh, for instance,
but a macro virus can infect any computer that supports a vulnerable application
program. The fact that Microsoft Word runs on many different kinds of computers
enables Concept and other macro viruses to move beyond traditional system
boundaries.
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