PDO とパスワード ハッシュはどのように PHP アプリケーションのセキュリティを向上させることができますか?

$dbh = new PDO(...);

$sql = "SELECT * FROM users WHERE username = :u AND password = :p";
$stmt = $dbh->prepare($sql);
$stmt->bindParam(":u", $_POST['username']);
$stmt->bindParam(":p", password_hash($_POST['password'], PASSWORD_DEFAULT));
$stmt->execute();

$dbh = new PDO(...);

$username = $_POST["username"];
$email = $_POST["email"];
$password = password_hash($_POST["password"], PASSWORD_DEFAULT);

$stmt = $dbh->prepare("INSERT INTO users (username, email, password) VALUES (?, ?, ?)");
$stmt->bindParam(1, $username);
$stmt->bindParam(2, $email);
$stmt->bindParam(3, $password);
$stmt->execute();