It's still up for debate in the SEO community whether or not popular search engines have a penalty for duplicate content. While some argue that it is a myth, others testify that they experienced a tremendous boost in ratings when they replaced any duplicated content in question. The main reason search engines may impose a penalty is to avoid serving nearly identical pages in their rankings, which could cause people to opt for different search engines.
To be safe, create original content for your website with a copyright notice to restrict others from using your content. Next, filter your website's content with duplicate content checking technology. You can also perform periodic searches for duplicate content on your website. Take action if you find issues. If other sites have copied from your website, use Google's archive dates to help determine publishing dates.