Search engine optimization helps the website to rank well in search engines such as Google, Yahoo and MSN for the keywords related to the business. Some SEO companies think that the addition of keywords again and again in the web pages will make the site visible on first page of search engines. Thus they duplicate the content on pages to achieve maximum number of keywords in an online market for the business of the company. But this does not happens as search engines filter out the duplicate content and the site owners suffer rankings and traffic losses. The text that appears on more than one uniform resource locator (URL) in the internet is duplicate content. If there are more than one identical content in the web portal, the search engines has to decide the original content link, and the web pages with duplicate content are rarely shown on Google, Yahoo and Bing.

There are four types of duplicate content such as identical pages, scraped content, product descriptions and articles distribution that are filtered out by search engines. The websites that are identical to another web portal on the world wide web are considered to be spam. The same content of many sites with different look and feel are filtered out by search engines. As the bloggers take content from the website and repack it to look different, the scraping applied to the blogs on the internet are becoming more of a problem for search engines. Many ecommerce websites in the market using the same description of the products is difficult for search engines to spot but still considered as duplicate content.

SEO experts believe that search engines also filter out the content similar in articles submitted to directories by different companies. When a search engine robot crawls a page of a site, it stores the information in the database and checks relevancy of the page. 

In order to remove duplicate content one has to make internal links consistent and minimize similar content throughout the website. Duplicate content is the complex problem and SEO experts identify as well as get rid of it without damaging SEO efforts. For the company with business across the globe and multiple web portals in different languages, there is a great possibility of content to be duplicated. Thus SEO experts carry out content check while applying SEO activities to the portals.