my $_Class_Data = "private stuff";
...
sub Class_Data () { return $_Class_Data; }

##</code><code>##

my $_Class_Data = "private";
...
# constructor
sub new 
{
	my $class = shift; 
	return bless(
		{	_Class_Data => \$_Class_Data,
			# other init...	
		},
		$class
	);
}