You want to disable anonymous comments right ? Well, guess what it has been asked just a few threads before you:

[url=http://forums.b2evolution.net/viewtopic.php?t=21172]Only registers put comments[/url]

Other than the fact that it has been asked a zillion times and that you didnt care to search, you could be able to spot it only if you just took a quick gaze at the first page.

No, I think they are asking about blocking robots without having users to register to leave comments. One way is through .htaccess keeping up with the new ones as they come along.

"without user id" suggests "limit comments to logged in users only" ;)

¥