Nothing to worry about... as an experiment, I have been running without a firewall on my Mac G5 for over six months to see what would happen (everything is backed up, of course), and so far, nothing has happened. Hackers hit and bounce.
That's good to know. Another question. When I went to eBay this evening they advise I upgrade to Firefox. Do you think this is a good idea? (iBook 2000 w/OS X, Safari 1.) Or should I upgrade Safari?