Hi there -- first off, thanks very, very much for WPBlacklist. It's keeping my blog free of comment spam, and I've recommended it to friends running WordPress. It's a great bit of work.
However, I'm thinking of changing a couple things in it, and I can't tell if I'm allowed to do that, or if I'm allowed to distribute changes. I've checked the files in the plugin itself, along with your blog, the download page and this support forum, and I can't seem to find any mention of a license.
WordPress itself is distributed under the GPL, which means I can change it and distribute those changes freely. Is WPBlacklist distributed under the GPL, or under another similar license?
Thanks again for your time and for your work.