Hi Paul,

Its nothing but a threat infection on your machine.

Check for autorun file from Start>Run>C:/autorun.inf

Incase you find , try to loate .exe file inside that and search on the system.

Submit the same to symantec tehinical support team.

Rgrds,
SAM

 its autorun.inf contains virus but its not detected by antivirus so you can disable the AUTORUN for all drives by configuring the registry. Open the registry by typing regedit.exe to the command prompt (if your still at the command prompt) or execute it in Run. Look for the HKEY_CURRENT_USER\Software\ Microsoft\Windows\CurrentVersion\Policies\Explorer as shown in the pic:
Double-click the NoDriveAutorun DWORD entry and type the value HEX: FF (255 in Decimal). (If the NoDriveAutorun does not exists, you can creat it by right-clicking the right side area of the regedit window, then click New->DWord Value -> type NoDriveAutorun) Close the registry and restart the computer. This procedure will disable all the autorun for all drives of your computer and at least will prevent the autorun function of infected USB drives or CDs and avoid the infection of viruses like the Bacalid and RavMon.exe.

If you want to prevent viruses that uses autorun.inf to infect your USB flash drive, try to do this:
1. Open your flash drive via Command Prompt (do this via Start->Run->cmd.exe)
2. Change your logged drive to your USB flash drive (e.g. if your drive is at drive E: then type E: on the command prompt then press enter)
3. Create a folder named: AUTORUN.INF on the root directory of your flash drive. (to do this type the command: MD\AUTORUN.INF). If an error: a subdirectory already exists… shows, try to follow the instruction above to remove existing autorun.inf before doing this instruction.
The reason why this will avoid future infection is that autorun.inf viruses usually generates a file autorun.inf. Having an AUTORUN.INF folder on the root directory of your drives will make virus programs unable to create their own autorun.inf file, virus can’t even overwrite it because it’s a folder and not a file

 here another solution for your problem:
Boot your system in Safemode
Open your flash drive via Command Prompt (do this via Start->Run->cmd.exe).
Change your logged drive to your USB flash drive (e.g. if your flash drive is at drive E: then type E: on the command prompt then press enter)
Type ATTRIB -H -R -S AUTORUN.INF then press enter
type in “del autorun.inf” then press [Enter]
After reboot, you can now access your drive.

Try creating a Read-only autorun.inf folder as an added precaution.