That's currently unsettled, and yes a lot of computer-crime experts (even typically law-and-order-leaning ones) consider it a huge problem--- it might actually be a federal crime to post a comment on a blog in violation of the blog's Terms of Service.

This case is currently winding its way through the courts, and will hopefully be overturned: http://volokh.com/2011/06/14/petition-for-rehearing-filed-in...