WPMu disable certain sidebar widget

Hi everyone,

I need to disable certain widget on every of my WPMu blog, specially the rss sidebar widget so users can’t add their spammy rss feed.

Found this _https://wpbits.wordpress.com/2007/06/15/disable-default-wordpress-widgets/ and found also using this code

add_action( ‘widgets_init’, ‘my_unregister_widgets’ );

function my_unregister_widgets() {
unregister_widget( ‘wp_widget_rss’ );
}

But it’s not working on wp 3.03

Any idea?