How to prevent unwanted comments or comment spam

Blogger is planning to introduce a spam feature for comments that will let you auto spam unwanted comments before they publish on your blog.A comment posted on a blog is considered to be a spam if it is posted for a commercial purpose.
The topic of the comment could be from a offering a miracle cure,friendship offers, online lottery scheme,tragic story of a girl with lots of money in bank account  etc.

Let see how it looks:

If you want to experience what it's all about,click on the link Blogger in Draft and click on the "Comments Tab".You can also moderate, delete and publish the real comments on your blog.

Tips to prevent unwanted comments

• Enable Word Verification for the comments.
• You can activate Comment Moderation feature of blogger that will let you see new comments and approve or reject them before they publish on your blog.
• Do not allow links with "rel=dofollow" tag in comments so that no Pagerank will be passed to the spammers.

Kudos to the blogger team for introducing such a good feature.