Hi Photon,
You are probably safe. From your description, it sounds like AutoProtect identified the downloader for that threat and stopped it before it could get installed on your computer.
It may be a good time to take some preventative action on the network --- I recommend making sure that all MS patches are up to date, SEP or SAV is up to the latest version, weekly scheduled scans are completeing successfully on all clients, passwords are strong and network shares secured. A little time spent now is better than a lot of work when an infection gets loose.
If any future issues are encountered, please do check back on the forum again or conatct Symantec Technical Support!
Thanks and best regards,
Mick