Duplicate content can often arise without our knowledge, despite our best efforts to prevent it. Here are 8 potential sources of duplicate content that could be affecting your site :
1. HTTP and HTTPS URLs
2. Sneaky scraper sites
3. Long lost subdomains
4. The "secret" staging environment
5. Dynamically generated parameters
6. Mirror subdirectories
7. Syndicated content
8. Similar content
Read more at: http://searchengineland.com/dont-get-du ... seo-258095