Firewalls are merely one minor step in the entire process of properly securing a network. The majority of people only set up the inbound rules and forget about the outbound. Also the majority of firewalls don't prevent MITM attacks, along with countless other methods.
Firewalls typically can't detect MITM attacks.
Knowing an ip address is no different than knowing someones home address. You still need to get through the door.
Like a home, any computer can be broken into. If security is a concern keep sensitive data on a non networked computer or external hard drive.
A good first few steps: not using windows, securing your browser. and securing your email.
If you REALLY want it 100% safe try also unplugging it, storing it inside a tamper proof safe inside a Faraday cage. Ever heard of TEMPEST?
http://en.wikipedia.org/wiki/TEMPEST
Well, it is hard to argue with the computer experts here, especially when one of them is a hacker with experience. I've already moved all my sensitive files from this computer.
If you want a good tip invest in an encrypted flash drive that you would keep on your keychain. Start using portable applications. Portableapps.com and if you REALLY want to feel more secure use a VPN connection it's pretty cheap. If you want to but that's a tad extreme instead of using another computer use a bootable linux distribution.
Here is my reasoning:
- Get your Firefox browser on your flash drive. It will NEVER touch your hard disk, which makes it pluggable into any other computer i.e no cookies or browser history to worry about.
- Keep it on your key chain. Unless you lose your keys often it would never leave your immediate location. and even if it did it would be hard to access.
- Pay for a VPN provider, your IP will permanently be hidden.
- Bootable linux would secure you against any viruses, trojans or keyloggers. It wont let anything get installed permanently to your hard drive and again you can just pop in a cd or dvd and have an operating system running in seconds.
Once you are done with those sensitive emails, photos, etc they will be saved on your encrypted drive and only you can see them. And once you shut down the computer there will be 0 forensic evidence of anything.
I could push my security a bit further using a ram drive but let's not go there...