65 How many viruses are there? (Computer virus)
Description
This article is from the Computer Viruses FAQ, by Nick FitzGerald n.fitzgerald@csc.canterbury.ac.nz with numerous contributions by others.
65 How many viruses are there? (Computer virus)
It is not possible to give an exact number because new viruses are
literally being created every day. Furthermore, different antivirus
researchers use different criteria to decide whether two viruses are
different or one and the same. Some count viruses as different if they
differ by at least one bit in their non-variable code. Others group
viruses in families and do not count the closely related variants within
a family as different viruses.
Further, some antivirus researchers have samples in their collections
that they count as viruses, but that several other experts strongly deny
are viruses. Sometimes these are "partial viruses", where a virus has
not properly infected a host and are therefore non-infective, other
times they are well-known non-viruses. As some of these non-viruses are
known to be in some of the common test sets, some antivirus software
vendors count them amongst the viruses they detect.
As of January 1995 there were about 5,600 PC viruses, about 150 Amiga
viruses, about 100 Acorn Archimedes viruses, about 45 Macintosh viruses,
several Atari ST viruses, a few Apple II viruses, four Unix viruses,
three MS Windows viruses, at least two OS/2 viruses and two VMS DCL-
based viruses.
Fortunately, few of the existing viruses are widespread. For instance,
only about three dozen of the known PC viruses cause most of the
reported infections and fewer than 200 PC viruses have been found in the
wild at all.
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