There is no real mechanism for upgrading from the "evergreen" 11.4 to the current 12.3
back up data
reformat to ext4 or LVM
do a new clean install of 12.3
-- use the KDE4 Desktop if you do not want to fight with the mess of Gnome3
OpenSUSE 12.2 still has 199 DAYS left
as for installing and running a AV program
they are looking for Microsoft Windows viruses
good for a mail server or to keep you from giving your Microsoft Windows friends a MS virus , hidden in a shared file .
ClamAV dose a great job for running a mail server
and for scanning downloads for MS windows viruses .
( clam is in the suse base repos )