Askimet is a plugin that usually installs with WordPress. To put is simply, it is comment spam blocker that uses a global database to and special algorithms to determine if comment submitted to your site are legit or not.
The fact is that the more popular your website gets, and the better it ranks in the search engines, the more susceptible it will be to spam comments. In this video I explain, why and how these spam comments are submitted on your site, and of course why Askimet is a great free WordPress plugin to filter these comments.
In my testing over the years, this plugin is great… and it is FREE… to get your Askimet API Key you can do so here: http://akismet.com/