Do you leave the doors unlocked at night? Do you allow Shoulder Surfing? Do you lend your Mac to others while you are away? Does everybody help themselves to your technology? Are you sure that DVD that neighbor burned for you doesn’t carry a trojan? In many ways these are obvious questions about common weaknesses. A firewall cannot protect you if you allow untrusted parties to have physical access. If you cannot say who was allowed to do what, no amount of magic or forensics can help you retrace how and if a compromise occurred. All someone has to do is stick a CD in, start your Mac in Target Disk Mode or take your hard drive away. They could just copy the drive and leave it all untouched, taking with them all your preciousness and you’d never know. Now you understand physical security. So even BEFORE you invest in a firewall and other “Recommended Software” or downloads, or scanners or whatever the nearest expert recommends, Secure the premises, and be aware of the activity in the perimeter of the system.