email security updates from microsoft and W32.Swen.A@mm virus

I have been gettng these security updates by email from
supposedly from microsoft, however, someone told me not to
do any thing with them but delete them. Miscrosoft does
not send sp's by email do they? I thought it was only
through the windows update function. In any case is there
a way to prvent these types of emails from jamming up my
inbox?
Also my NAV has been consistently picking up the virus
W32.Swen.A@mm. I have been quarantining it and then
deleting the contents of the quarantine folder, since
Symantec already i