Remove WordPress generator meta tag

functions.php

// Remove WordPress Generator Meta Tag
function remove_generator_filter() { return ''; }
if (function_exists('add_filter')) {
 $types = array('html', 'xhtml', 'atom', 'rss2', 'rdf', 'comment', 'export');
 foreach ($types as $type)
 add_filter('get_the_generator_'.$type, 'remove_generator_filter');
}

// Another option:
function qr_remove_wp_version() {return '';}
add_filter('the_generator', 'qr_remove_wp_version');