wow, thats just a little paranoid.
Unfortunately it isn't THAT
paranoid. If I remember correctly, 1-2 years ago, a research was done called "Project Honeypot" (or something like that) to how "unsercure" the internet was. Within 15 minutes from being connected to the internet, the PC was being port-scanned and within the hour the PC was compromised.
When my PC used to be connected directly the the internet (no NAT router), I was doing the same thing; I downloaded firewall and antivirus prior to formatting and plugged the network cable back only when the firewall and antivirus were installed. I also did the same thing when I was at my parent's because I didn't trust other PC in the network to be clean :P.