If you write online, on a blog, on Twitter, on Squidoo, even in the comments section of a site, you are a published author.
Before you write something negative about another person, you need to realize that the casual nature of your post doesn’t protect you from a lawsuit. Charles Glasser is an expert on this and a new edition of his book just came out. You should consider reading it, or be sure to hire an editor who did. It’s more sophisticated than a quick overview, but you know you’re getting the straight scoop.