I've just enabled the new virus scanning option for groups. Under Message Policies, there's a dropdown labeled Viruses. It defaults to Blocked, but can be set to Moderated.
I disabled scanning for phishing schemes, because the false positive rate was just way too high. So it only scans for viruses. Emails from non-members that contain viruses are blocked regardless of the group setting. When a message is blocked or moderated, an entry is added to the activity log (there are 3 new actions: non-member blocked, member blocked, member moderated). When viewing a moderated message for approval, a red badge is displayed with the name of the virus detected. I'm not currently retroactively scanning the archives and I'm not currently displaying anything when viewing moderated and then approved messages in the archives.
In my testing, very few viruses are actually sent through the system. So, hopefully, this is something you won't encounter.
Please let me know if you have any questions.