While handling of global variables had the focus on to
be easy in PHP 3 and early versions of PHP 4, the focus has
changed to be more secure. While in PHP 3 the following
example worked fine, in PHP 4 it has to be
unset($GLOBALS["id"]);. This is only one issue of global
variable handling. You should always have used $GLOBALS, with
newer versions of PHP 4 you are forced to do so in most
cases. Read more on this subject in the
global references section.