Spam is a big problem in blogs. Some bots spam to get backlinks. Sometimes its hard to decide whether the comment is the spam or not. Here are simple plugins to set auto protection for spam for WordPress. If your site is linking to bad sites it downs your reputation in search engines.
Akismet is a pre-installed plugin in wordpress. It is coded by same company who is behind wordpress. But before you go through activation process of Akismet, I recommended you to install another plugin named cookies for comment (or known as comment for cookies)
Cookies for comment is a smart web development. It knows that spammer bots can’t have cookies storing facility, cookies are only available at real user end who uses a web browser.
The plugin adds an extra cookie and checks if the browser if having it before posting comments. More than 99% of spam comments on my blog gets blocked by this plugin.
The plugin allows you to choose between directly delete or mark as spam for suspected comments.
Though Akismet is not completely free for commercial usage. You need to configure Akismet and install your license key before you can use it, also known as API key. You can grab the API key from the official website akismet.com
I use only the above two plugins for comment spam protection. They do satisfactory work for me giving me complete freedom from spam.