This method was working in 11.x , I haven't checked for 12.x
open C:\ProgramData\Symantec\Symantec Endpoint Protection\CurrentVersion\Data\Definitions
you wiil find numbered folders for each virus defs till date
copy all the contents of the dated folder
create a new folder called incoming on the target computer you want to update
paste it inside
restart smc service.
Keep us posted