Hide Category

Hello,

is there any way to hide specific categories in the main blog.

E.g. I do not want to display the category 28 in the main blog.

I tried several tricks, like editing the functions.php:

function exclude_category($query) {
if ( is_page_template('blog.php') ) {
$query->set('cat', '-104');
}
return $query;
}
add_filter('pre_get_posts', 'exclude_category');

did not work…. Probably I did not get the template name right or it has to be done some special way with avia-framework….