Google’s duplicate content penalties can feel like strict punishment for web-sites that get attacked. Most marketers are aware of these actions and run their sites accordingly. However, what is not well-known among SEO circles is what actually constitutes duplicate content and how domain owners can be certain that their web sites are in compliance. A web site owners worst nightmare is finding out the hard way that their search ranking has been lowered and that theyve been removed from Googles index altogether. One way to play it safe is to make sure that you grasp the idea of duplicate content and that youre not in violation of Googles policies.First, you should know that Googles grounds for punishing those with duplicate content are actually quite reasonable. The fact is, Google wants to avoid search results pages overwhelmed by websites with the same or similar content, and with good reason; duplicate information makes it difficult for searches to find what theyre looking for.Google created a new patented fingerprinting technology to prevent the appearance of duplicate content on different websites. By recording an initial fingerprint of a site, Google can periodically compare the fingerprints of various sites in a database and lower the value of sites with content copies.There are several examples of web sites and web site content that can be considered duplicate and, surprisingly, youll find that most are unrelated to spam. Here are just a few:Viral Content: The most common case penalized by Googles duplicate content policy is using PLR articles or other free articles in exchange for a link.Mirrored Sites: Its quite common to mirror a site in order to balance the amount traffic on the server and enable sites to divide hits received between two identical sites. This practice is effective in balancing server load and eliminating downtime in loading, but the site copies are considered duplicate content.Lets say you own the .com, .net, and .org versions of your URL or versions with common misspellings of your URL. Rather than only redirecting traffic to a single URL, it may be wise to include some of your content, a newsletter, or free downloads on these pages.Sub-Niche Domains: If you have a sub-niched site, you should use subsets of keyworded content. For example, if you write articles on personal finance for single moms, you may want to leverage your articles by creating sites targeted to special topics, such as single-moms-savings-tips.com and single-moms-debt-help-tips.com. Dynamically Generated Content and/or Templates: The use of RSS feeds from blogs and news/article syndicates amount to a greater amount of duplicate content on web sites. Dynamically generated templates in Content Management Systems (CMS) or shopping carts may also register as duplicate content. NOTE: This example applies only to feeds that display as static HTML. If youre using a javascript feed to attract visitors, it cant help your SEO, but it also cant trigger a duplicate content flag, since Googles bots cant read it anyway.