Read about other user's problems a while ago with the ZA Security Suite Update starting up when it feels like it and then slowing everything down to an impossible crawl. I also seem to remember that something's in the pipeline so after re-installing a least 4 times I'd more or less given up, that is until this morning when the scanner started which was ok as I'd already scheduled it. However for some reason I set it to Pause and then completely forgot about it ! Wonder of wonders ! No hourly updates and all my work done on time. I then noticed the scan and finished it at which point the Update appeared !
Being in a generous mood I let it go ahead of course ! All I know is it works for me !!