to automatically uncompress it with the CURLOPT_ENCODING option, libcurl
  could wrongly provide the callback with more data than what the maximum
  documented amount. An application could thus get tricked into badness if the
  maximum limit was trusted to be enforced by libcurl itself (as it is
  documented).

  This is further detailed and explained in the libcurl security advisory
  20100209 at

    http://curl.haxx.se/docs/adv_20100209.html