Improve the user registration system to incorporate password hashing and salting techniques for enhanced security of user credentials.

<form method="POST" action="register.php">
        <input type="hidden" name="register" value="true">
        <input type="text" name="username" value="<?php if (isset($_SESSION['username'])) echo $_SESSION['username'] ?>" placeholder="username">
        <input type="password" name="password" value="" placeholder="password">
        <input type="password" name="confirm_password" value="" placeholder="confirm password">
        <input type="submit" name="register" value="Register">
</form>