gistfile1.php

<?php
// via https://twitter.com/joswr1ght/status/544548300033363971

var_dump(md5('240610708'));
// string(32) "0e462097431906509019562988736854"

var_dump(md5('QNKCDZO'));
// string(32) "0e830400451993494058024219903391"

var_dump(md5('240610708') == md5('QNKCDZO'));
// bool(true)

var_dump(md5('240610708') === md5('QNKCDZO'));
// bool(false)

// Why? 
// $a == $b   : TRUE if $a is equal to $b after type juggling.
// $a === $b  : TRUE if $a is equal to $b, and they are of the same type.
//
// When Type Juggling for the comparison, if PHP sees a string that could be
// a float, it does treat it as a float. In this case, "0e"-something will
// always evaluate to 0 (as 0 × 10**n will always be 0), evaluating the
// comparison to TRUE:

var_dump("0e4" == "0e8");
// bool(true)

var_dump("0e4" === "0e8");
// bool(false)

// Reference:
// http://php.net/manual/en/language.operators.comparison.php
// http://php.net/manual/en/language.types.type-juggling.php
// http://php.net/manual/en/language.types.string.php#language.types.string.conversion