Magento and Duplicate Content
When pages with the same (or very similar) content exist as different URLs, this is duplicate content. Google can detect this and may decide to list only one of the URLs in its search results.
In Magento, products can be found using the URL
For every category that this product appears in, the same product can also be reached through
If your products exist under more than one category, the duplicate content problem is increased, but there is something you can do to improve this.
'System' -> 'Configuration' -> 'Catalog' -> 'Search Engine Optimisations' and set ‘Use Categories Path for Product URLs’ to ‘No’. If you do this, it is worth remembering that you lose the category title keyword from the URL, so perhaps you will want to make use of the ‘link-url’ field on the product to re-introduce these words to the URL.
In the same section you should set ‘Use Canonical Link Meta Tag For Categories’ and ‘Use Canonical Link Meta Tag For Products’ to ‘yes’.