If you have a feeling that someone has copied your website or blog content you should check for duplicate content immediately before it may hurt your search engine ranking. Google does not like duplicate content and could exclude the pages that have been duplicated from the search engines. So once in a while you should check if some of your most popular web pages have been copied from some other website or blog.
You can check for duplicate content manually by copying a couple of sentences from one of your pages and then paste it into the search field on Google. When you hit the search button you should find your own website at the top spot but if Google also returns other results that have the same sentences on their sites, your website content has been copied which is plagiarism and illegal.
Go to Copyscape.com to search the web for duplicate content. All you need to do is to type in the URL of the page you would like to check and then press go. It will then tell you if any websites were found. Copyscape is a very well-known site and is free to use.
You need to copyright your website content to make sure that it is safe. When your site is protected by the US Copyright Office you will be able to prove that you are the owner of your content if anyone should ever copy your content.
If you do not have enough money to afford a paid copyright option, you can always use the free method where you just write copyright, the year of the publishing and then your name. Now, this is far from as good as the paid option and may not even be enough for you to win the case if someone steals your content, though it is still better than nothing.