Perl Security: 5. When using functions, remember...
GLOBs

Namespaces don't only manage the previously mentioned data types. For example, filehandles are also entries in the namespaces... Only they don't have a sigil ($, @, %, &) to be grabbed by.

GLOBs are references, all right, but not to a specific type - They are references to anything. Their main use is to pass around file descriptors.

Try not to use them. Nowadays you have a cleanly OO implementation for filehandles: IO::File
my $handle = IO::File->new();
$handle->open('<filename') or die 'Ouch!';
use_a_file($handle);

Being $handle a lexical variable, it will be destroyed (and cleanly closed) as soon as it goes out of scope. Many operations are also managed much more intuitively this way.