public function exists($password = null, $since = null)
	{
		$db = \App::get('db');

		if (empty($db))
		{
			return false;
		}

		$query = "SELECT `passhash` FROM `#__users_password_history` WHERE user_id = " . $db->quote($this->user_id);

		if (!empty($since))
		{
			$query .= " AND invalidated >= " . $db->quote($since);
		}

		$db->setQuery($query);

		$results = $db->loadObjectList();

		if ($results && count($results) > 0)
		{
			foreach ($results as $result)
			{
				$compare = \Hubzero\User\Password::comparePasswords($result->passhash, $password);
				if ($compare)
				{
					return true;
				}
			}
		}

		return false;
	}