Brian is correct. Please vote up this Idea:
https://www-secure.symantec.com/connect/idea/scan-results-displayed-sep-mac-clients-sepms-reporting-needs-expansion
I hope this is an isolated incident for you. What I would do is open the log on the client (under Tools > View History). It'll show Date, Location (hover mouse over for full path), virus, and status. It unfortunately can't be exported (believe me, we find that frustrating too). I would be surprised if it were anything but a detection on a Windows-based virus residing on the Mac file system; my bets are on an email attachment.
sandra