As mentionned in above posts,you should submit any potentially infected file which is undetected to security response.
You could also upload the file to virus total or threat expert,it COULD potentially be a false positive.
Symantec will issue updated virus signatures only if you submit these.
Remember a 100% detection rate for all existing malware is not feasible.What is more important is to detect and remediate 100 % of in the wild malware,a smaller set of malware which is most likely to be encountered by end users.
Safe computing practises and user education is crucial to limit exposure to malware.
Keep windows,your browsers and its plugins and other third party software up to date.this should suffice together with an up to date SEP 12.1
http://www.virustotal.com/
http://www.threatexpert.com/