If you are running your own blog (you have installed www.remarpro.com software on your server), every single word that you publish is owned by you. You and your content are protected by the fullest extent of copyright law in your country. Unfortunately, that also means that it’s up to you to police any illegal usage of your content.
Splogs, blogs that re-post content from the feeds of other blogs for the purpose of generating ad revenue, are unfortunately quite common. The best thing you can do is install a plugin like Better Feed and use that to attach a copyright notice and a link back to your blog beneath every post in your feed. Even if your content is stolen, at least people will know who it belongs to. If the splog is using Google Adsense, you can click the “Ads by Google” link at the bottom of the ad and report that the blog in question has stolen your content.
If you are using a wordpress.com blog, you’ll have to contact their support forums to ask what preventative measures they offer.
For more info on policing the usage of your own content, read this article and this article.