Hacking, in the sense of a remote compromise of a networked or local compromise of a computer, is your data being accessed by parties unknown. Hacking has evolved from simple phone phreaking (ever wonder why cyberphreak.com is spelled with a ph?) to curious individuals, to corporations, to, now, entire governments being behind and subject to hacking.
I have been using computers for over 30 years and there is one thing I know: If someone wants your information, they will get your information. I don’t care how many firewalls or intrusion countermeasures you have, what operating system you are running, or hardware you are running; if it is networked, they can get in. If they can get local access to your machine, they will get in.
If it is hopeless, what can you do to keep sensitive information? You will need 3 things: A writing implement, such as a pen or pencil, paper, and bad handwriting. If it really matters, get a blank book, write it down in handwriting only you can read, and put that book in a safe place. Even if your home is broken into, it will be difficult to decipher the information. If the book is stolen, well, you know what was written down in there and exactly what was lost. At least with your poor penmanship, a human will have to painstakingly decipher your chicken scratch. You can also destroy the book in a fire and grind the ashes.
If you must use a computer, DO NOT NETWORK THE COMPUTER. DO NOT INSTALL A WIRELESS CARD. Have a specific computer that will never be connected to the internet, ever. Yes, very 1983, but what else can you do? DO NOT STORE SENSITIVE FILES ON A HARD DRIVE. Keep all files, encrypted, on a device that can be easily destroyed. Something like a micro-SD card. Tiny enough to hide anywhere, small enough to be destroyed if the need arises. A cross cut paper shredder will do. Someone with enough time and money might be able to get information using a scanning electron microscope, then decrypting the data, but, seriously, what are you doing to deserve that kind of attention?
If these steps seem a little extreme, they are. The paper/book based is my personal choice, and I have really bad handwriting. It can never be hacked remotely and I don’t write anything down that is illegal anyway, just personal that I don’t want strangers to see. Turns out that little diary or journal you kept as a kid is the most secure choice after all.