Minecraft premium checker

import urllib, sys

url = "http://www.minecraft.net/haspaid.jsp?user="
users = open(sys.argv[1], "r").readlines()

for user in users:
  user = user.strip()
  s = urllib.urlopen(url + user).read()
  if "true" in s:
    open("premium.txt", "a").write(user + "\n")
    print "Premium Account: " + user