WordPress is now used for much more than a blog. Themes are setup to utilise the post functionality in many ways. Bots exist which will bombard your site with spam links. You can blog these by default by unchecking the following:
Settings > Discussion > Allow people to post comments on new articles
Register Your Akismet Plugin
You will most likely have Akismet installed as part of you WordPress installation. Ensure that this plugin is activated and your API key is registered. It’s free if it’s for personal use so get your site spam protected right away!