From: engelbert_buxbaum@hotmail.com   
      
   Raymond Holtzfingeru wrote:   
      
   > Hello,   
   > I am trying to write a program that will open an executable file and   
   > write a value to it to act as a counter to see  how many times the   
   > file has been run.  After the file has run a set amount of times, I   
   > want to make the file inoperable.  What would be the safest way to   
   > determine where to write that value?  Maybe seek to the end of the   
   > file and then step back a few bytes, something like seek(filename,   
   > filesize(filename) -4)?  Is there a better/safer way to do that?   
      
   Hm, usually such schemes are a waste of time. But technically it is   
   certainly feasible for a program to write a value into its own exe-file.   
   This has been used by the zerberus-unit to write a check-sum of the   
   program into its code on first run. On all following runs, that check   
   sum would be compared with the current value, any change indicating a   
   virus-infection. Probably no longer as important since classical viruses   
   are no longer as rife as they were 10 years ago (macro-viruses and worms   
   are now more significant). See A. Schäpers, c't 7/92, page 146-152 for   
   the code.   
      
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