I thought for a while if I should answer this question, because
it's clearly listed in the FAQ as a question that you should never
ask here, but I think that old Macs is something of a novelty here,
so here we go..
What, excactly, is an old Mac? I think my mom's old Mac Classic from
sth like over ten years ago is pretty secure, because it hasn't
been networked for approx five years. ;-) (The Mac, my mom is very
much alive and socializing.)
If you plan to run an old Mac as your firewall, I think that
OpenBSD is a more secure solution, but someone else might have
something different to say on this.
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Heikki Korpela -- heko_(_at_)_saitti_(_dot_)_net