qsf()
  Quick Spam Filter scanner.
  
  This scanner scans for spams. If a spam is returned, a string
  SPAM is returned as virus name. It uses Quick Spam Filter.
  
  Usage: qsf(['/usr/bin/qsf','-r'],SPAMSTRING='',MAX_FILE_SIZE=500000)
  
  Where: in [] is a path and argumets of qsf binary
         SPAMSTRING is a string, which define a report string,
           which is checked. If it is found, mail is assigned as 'SPAM'
         MAX_FILE_SIZE is a number, which defines maximum file size,
           which can be tested. If a mail (with header) is larger,
           it is not checked (by default 500000).