Last month I installed version 3.0.566 of NOD32 onto the DC (running WS2k3) of our single server network, upgrading from version 2.7. The installation went smoothly, and everything seemed ok until several hours later when network access to the sever effectively "locked up", meaning that users could not access shared files and there were huge logon delays as clients were unable to access GPO information. Rebooting the server did resolve the issue, but only for it to recur after approximately a day. After going through the cycle a few times, I removed version 3 of NOD32, replaced it with the old version 2.7 and everything has been fine since. My research of the issue leads me to suspect the kernel mode filter driver used by NOD32 (indicated by Microsoft KB articles 908370 and 816071). We (read: management!) are keen to upgrade to version 3, and I note that there is now an updated release of NOD32 available – however as the release notes only list GUI & mail client fixes I don't want to install again until I'm confident that the above issue won't recur.