One of the things I would like to use the viewer for is to view attachments to emails that are in the attachment directory for that program. Sometimes those attachments are old or I don't recognize them and want a safe way to view them to determine what they are, without potentially infecting my PC. Am I correct in presuming that viewing a file with the Opus viewer is safe, that even if it is a virus or trojan or whatever, that the viewer will not open it and create problems for my machine?
I wouldn't bet on that. Opus might use DirectX as a part of the previewing process (for example), so every flaw, that could be exploited when using IE could be present during the usage of the preview in Opus as well.
The best thing would be, i think, to leave that to some virus scanner, & remove suspicious attachments in the first place.