Creating file on login

[Fausto <fausto () pix com br>]

   I have a system that when one try to login it create a file with the 
name of the user that tried to log.
   The problem is that if the do not exists the system creates the file 
with the invalid user...
   Can we do some exploit in this case...??
   Is this problem dangerous...
   Fausto Catvalho


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