sub new{
    my $class = shift;
    my %att = (
        name  => 'Foo',
        vname => 'Bär',
    @_);
    bless{
        name => $att{name},
        vname => $att{vname},
        USER => {}
    }, $class;
}

sub add{
    my $self = shift;
    my $att = shift;
    my $val = shift;
    $self->{USER}{$att} = $val;
}

my $m = main->new(name => 'booooo');
$m->add('PLZ','12345');
puts Dumper $m;

# das gibt aus:
$VAR1 = bless( {
                 'USER' => {
                             'PLZ' => '12345'
                           },
                 'name' => 'booooo',
                 'vname' => 'Bär'
               }, 'main' );