In the post he said he uses a plugin called WP-HashCash. The main advantage of this plugin is “it requires no maintenance or intervention on my part, and it’s invisible to my readers”.
He went on to explain:
Intrigued at the prospect of a maintenance-free spam solution and taking him at his word on its efficacy, I have installed WP-HashCash and disabled Spam Karma.
I am combining this with the blacklist feature of WordPress 1.5 (which will require a little maintenance) and I am moderating comments until I am confident that WP-HashCash is the solution I have been looking for.
Roll on a spam-free blogging experience!