Sometime in your life you will be involved in an accident, hopefully a minor one. The same is true with a computer, sometime while using a computer you will be attacked by a virus. Personally I have received around five attacks on my personal computer in the past ten years where I have been on-line, my virus software protected me every time. Keep your virus checker updated, I don't know of any virus checking software that does not give you free updates via the internet for at least a year. Use the software that comes with your computer.
Every computer sold has some parental controls built into the operating system.
Children DO NOT have private passwords, only the parents do. Remember who should be in control. Sorry, your parents first responsibility is to the safety of their children. It is not always a trust problem with you but a lack of trust to the other people in the world that wants to harm your family. Where you live, go to school, phone numbers even your name.