portable? yes.

secure? no.

when you run it on a program it changes it to something like:

#! /usr/bin/perl

my $prog = '';

{
    my $key  = 6;
    local $/;

    $prog = pack "c*",
             map { $_ ^= $key }
             unpack "c*", <DATA>;
}

eval $prog;
__END__
# a bunch of packed data here
[download]

if you change the 'eval $prog' to 'print $prog', you get the original source code back.

anders pearson