Used by millions of websites, Akismet filters out hundreds of millions of spam comments from the Web every day. Add Akismet to your site so you don't have to worry about spam again. Sign up for an Akismet plan (A free plan is available) that best suits your needs.
Once you have a 'Key', enable Akismet, enter your key, then chose where to use spam protection.
The plugin checks the following for spam:
The plugin sends the store URL, current page, customer IP address, Customer user agent, user referrer, comment type (comment, contact form, etc), customer email (when available), customer name (when available), and of course, the actual comment text - then Akismet returns with either spam or not.
This is a free version and does not store 'spam' for moderation.