That’s actually quite a difficult question to give a straight answer to, because you could answer it either way. Yes duplicated content can harm your website rankings, but in some instance it won’t. We’ll try and explain that a little clearer. In Search and More’s opinion the important point is that you look at what the duplicated content is, and then examine what the purposes of posting the content is.
If the duplicate content is there simply to manipulate and artificially inflate the search engine rankings, then you need to address this urgently. The key to all content on your website is to add value and provide information that the reader will find useful. It should also be remembered that the content is meant to be read by a human being: don’t make the mistake of writing solely for Google or the search engines and disregard the end-user. Duplicated content will turn both the search engines and the reader off, and that’s the last thing your website wants.
If your duplicated content is product descriptions then this will not harm your rankings.
Although technically duplicate product descriptions should be penalised under the Panda update and Google’s new fresh content algorithm, they rarely are. If problems are experienced, then there are ways of restructuring your website to address these issues. In many ways there are some potential advantages to creating unique product descriptions where possible. Our advice would certainly be not to use product descriptions that are worded in exactly the same way as competing websites. It’s much better if you can create product descriptions that are different, but this shouldn’t be attempted if it will impact on any otherwork carried out on the website.
If your site contains multiple pages with largely identical content, there are a number of ways you can indicate your preferred URL to Google. This process is called “canonicalisation”, and is explained on Google’s support pages: http://support.google.com/webmasters/bin/answer.py?hl=en&answer=139066
If content is deliberately duplicated across domains in an attempt to manipulate search engine rankings or win more traffic, then Google will take action. Google sees such practices as deceptive and argues that they result in a poor user experience. Google’s algorithms are now predominantly geared to giving the user the best experience. Google aims to index pages with distinct and unique information. If Google identifies instances where it feels the duplicated content is intended to manipulate the search engine rankings and deceive users, then it will make the appropriate adjustments in the indexing and ranking of the sites involved, meaning the site may suffer, or might be removed entirely from the Google index, in which case it will no longer appear in search results.
For the steps you can take to rectify the issue on duplicated content see Google’s Webmaster Tools page: http://support.google.com/webmasters/bin/answer.py?hl=en&answer=66359