Super simple spam protection for Ruby on Rails

new.html.erb

<% form_for @comment do |f| %>

  ...
  
  <p style="width: 1px; height: 1px; overflow: hidden;">
    Lämna följande fält tomt:
    <%= f.text_area :comment %>
  </p>
<% end %>

post.rb

class Post < ActiveRecord::Base
  attr_accessor :comment # fake attribute used for spam trapping
  validates_length_of :comment, :in => 0..1
end