Avoiding Guest SPAM effectively

[Alenônimo]

Could I make an request?

I use on my site an mod called "No Spam by Guests! 0.1". I never had another spam after that. Never.

This MOD doesn't let an Guest post any links. Just that. It shows an message to the guest user saying that posting urls aren't allowed unless you're an registered user.

It's so simple that it should be on the core. It works wonderfully!

Edit: I forgot the link to the MOD - http://custom.simplemachines.org/mods/index.php?mod=369