Documentation:WordPress Basics/Basics 2 Guide/Fighting Spam
A great benefit of moderating comments is to prevent spam from being published on your blog. Many spammers use bots to automate certain tasks such as fill out forms or make randomized linked comments.
As mentioned before, you will be able to mark a comment as spam by going into Comments and hovering over the comment you are suspicious of. When a series of actions appear under the comment, just click spam and it will be transferred to your spam folder. WordPress will automatically take note of the email and IP addresses that those spammers leave. Future messages will then be blocked.