先举一个简单的PHP防注入的例子。假设有一段用户登录的验证代码：

<?php
$user = $_POST['username'];
$pass= $_POST['password'];
$result = "SELECT * FROM users WHERE name = '$user' AND password = '$password'";
if($row = mysql_fetch_assoc($result)) {
  //authenticated
}
?>

此时坏蛋用户只要输入下面的用户名和密码：

$user = "Dantago !Noabes";
$pass = "x' OR 'a'='a";

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