This article is from the Computer Viruses FAQ, by Nick FitzGerald n.fitzgerald@csc.canterbury.ac.nz with numerous contributions by others.
A CAVITY VIRUS is one which overwrites a part of the host file that is
filled with a constant (usually nulls), without increasing the length of
the file, but preserving its functionality. The Lehigh virus was an
early example of a cavity virus.
 
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