Add code to automatically update copyright date in footer

I’d like to make the copyright year update automatically.

Here’s some code to do it: http://www.updateyourfooter.com/

I’d use this:

© <?php
$fromYear = 2008;
$thisYear = (int)date(‘Y’);
echo $fromYear . (($fromYear != $thisYear) ? ‘-‘ . $thisYear : ”);?> Company.

Where in footer.php could I add it? How can it be protected from being overwritten in future WP upgrades?

Thank you!