The reason that my simple virus protection scheme was limited to *.COM 
files is that *.EXE files are actually modified by the loader.  For example, 
the segment addresses must be installed by the *.EXE loader when the *.EXE 
file is loaded into RAM.  This same program could easily be corrupted and 
used to infect the executable code with a virus.  I could see not simple 
means of detecting that such happened.  
  A CRC or checksum routine that verifed the integrity of the executable code 
before that code executes could not be used in general purpose *.EXE programs 
since the CRC and checksum routines do not know what legal values would be 
assigned to instructions accessing Segment Registers.
--- Maximus 3.01
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