> I access the internet via DSL from Verizon, > > I don't use a router, nor have I activated a Firewall.
Others have answered your questions. I'll just note that when my mother-in-law got Verizon DSL a few years ago, the DSL modem they sent here had a router built in (a wireless one even). So it is possible thet you might have a router without particularly being aware of it as such. Admitedly, Verizon probably ships multiple different kinds of DSL modems, so the one you got might not also be a router.
(The default configuration Verizon sent my mother-in-law had the wireless access wide open on their router, which I thought was a lot bigger security issue for her. I fixed that for her.)
If you don't have a router, I consider one generally a good idea anyway, even if you don't strictly "need" one. It isn't as though they are very expensive (certainly not compared to your 24" iMac). Security aside, it will be handy if you ever want to add another computer, or friends/relatives/whatever come over and you want to let them acess the net with their laptops, or... lots of other things.
-- Richard Maine | Good judgement comes from experience; email: last name at domain . net | experience comes from bad judgement. domain: summertriangle | -- Mark Twain
