Duplicate content? or not?

[titanium]

I recently changed the menu on my J2.5 site and added a further drop down menu before reaching the articles, in an effort to make them easier to find for the user; i.e. by grouping the articles into 2 subgroups. I didn't change their categories as I didn't want the URLs to change. However I now see that in my Webmaster Tools I'm being scolded for duplicate meta and in each case the article appears twice - once with a URL as before and once with the new menu item name prefixed.

Something tells me this is not good!
However when I ran a test page through a duplicate content checker website it didn't pick up the 2nd article.

What is the best way to remedy this? Should I just use the Joomla redirect function? If so, this seems incredibly clunky. Is there no way to change the menu structure without changing the URLs at the same time?

 

[Nochexman]

I'm certainly no expert, but look up "canonical links". I'm sure a real technical expert will be along in no time!

 

[iDigLocal]

Yes you need to set the canonical link for the url you wish to use for the website