What about nested comments, however? It's much better to use a module for something like this, rather than try to work out your own regex.

use strict;
use warnings;

$_ = join '', <DATA>;
s/<!--.*?-->//gs;
print;

__DATA__
<!-- comment -->text
<!-- multi-line
comment -->text2
<!-- nested <!-- comment --> -->text3
[download]

returns...

text
text2
 -->text3
[download]