difference between read only and view only for downloading the document

Can you please tell what's the difference between Read Only and View Only in sharepoint.

As per my requirement, my end users who have been assigned View Only should NOT be able to Download the document from a doc lib.Whereas who have Read permissions should be able to download.

But when i tested with few users with these permissions, those users who are having viewonly permissions was able to download the documents.

My customer worried about the download-the-document part. As per them end users who have view only permissions should not download the docs. how to achieve this in sharepoint. help is appreciated