Download the file <date>-<revision>-core15i32.exe where <date> is the current date and revision is the current revision of virus definitions. For example: 20150505-033-core15i32.exe
Navigate to C:\ProgramData\Symantec\Definitions\SymcData\virusdefs32\ (Note that ProgramData is a hidden folder by default, in order to see this folder Windows must be configured to "Show hidden files and folders").
Create a new folder called "incoming"
Open a command prompt (Start -> Run, cmd)
Navigate to the location of the intelligent updated downloaded in step 3 (cd <filepath>)
Run the command <intelligentupdatername>.exe /extract "C:\ProgramData\Symantec\Definitions\SymcData\virusdefs32\incoming". For example: 20150505-017-core15i32.exe /extract "C:\ProgramData\Symantec\Definitions\SymcData\virusdefs32\incoming"
Wait for 10 minutes. The SMSMSE should now reflect the new virus definition date.