write40.py

from sys import argv, exit
from struct import unpack
from StringIO import StringIO

if len(argv) != 2:
    print '[*] Usage: python', argv[0], '<arc>'
    exit()

fp = open(argv[1], 'rb')
fp.seek(6)
buf = fp.read(2)
num = unpack('H', buf)[0]

print '[*] Number of files :', str(num)

fp.seek(0)
buf = fp.read()
fp.close()

fbuf = StringIO(buf)

list = [x * 80 + 87 for x in range(num)]

for i in list:
    fbuf.seek(i)
    fbuf.write(b'\x40')

fp = open(argv[1] + '_', 'wb')
fbuf.seek(0)
fp.write(fbuf.read())

print '[*]', argv[1] + '_', 'saved'