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(unset($GLOBALS["id"]));. This is
only one issue of global
variable handling. You should always have used
newer versions of PHP 4 you are forced to do so in most cases.
Read more on this subject in the
global references section.