anti troll plugin

My friend has a blog. It’s very popular. One of the reasons for its popularity is that people don’t need to register, create an account, or have their posts approved before they’re displayed. Her blog works well 99.9% of the time.

However, there is one person that sometimes post as many as 10 on one thread. Normally that’s ok as we don’t believe in limiting but he often picks a fight with the other regulars. My friend got tired of this and told him that he now has a two post limit. If she sees more than this than she deletes his post.

I think this is ideal to keep it a manual process like this and to not make it happen automatically. However, there is no stopping him from changing his name and posting again.

Is there a plugin that will display the IP address? (not displayed on the form but for my friend to see? This way the troll has to change computers instead of only changing his name in order to fool my friend.