Hi,
You need to make that product "uncategorized".
Don't choose any category for that particular product.
Then with an URL, you can secretly open that product.
Here is how:
1- Make sure:
Show uncategorised child products in search results and modules? is disabled
Attachment Pasted_Image_1_30_14__10_15_AM-4.png not found
2- Open the product and remove the categories. Then choose -uncategorized-
Also, please note its product ID number.
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3- This product will be completely invisible in your fronted, but you can secretly open this product through this URL:
www.yourwebsite.com/index.php?option=com_virtuemart&view=productdetails&virtuemart_product_id=29
(the number at the end of the URL represent the product ID number, in my case it is 29, in your case it will be different)
Regards,
Support