Hmmmm...
I can only speak from what I've seen and heard from others...and don't have any first hand experience with ZA except a few times I ran it on Windows. Same with McAfee. 99.9% of my internet work is on a Mac, and I have no Anti-XX programs other than my router firewall. I've heard ZA is a very good program, but requires a bit of "tweeking" sometimes to max performance on a users machine/IPS/etc.. When that's done, most all love it.
Wish I could help more, and will post anything I come across. I do know that a many problems are cured recycling your router/modem, clearing cookies and cache from time to time.
Greg