One of the MS updates probably turned on MS's own firewall/av, thereby making Symantecs unnecessary. If you check by hitting START, then WINDOWS SECURITY CENTER, it should tell you whose stuff is running.
Since I work for IBM, I have to use Symantec stuff and so all my MS antivirus is turned off (see photo below), incl automatic updates (which come from corporate after they are blessed for exactly the same reason). Do you have a "safepoint" that you could roll back to?