v0lume:
1. Back up all important data onto an external HD.
2. Obtain (if you don't already have it) copies of antivirus and antispyware programs on CDs. If you're using programs you downloaded from the internet, save them on a thumb drive or something so you can have them ready to install without having to get on the Internet to download them again.
3. Wipe your computer's HD and re-install Windows. Make sure that it's not hooked up to the internet at all.
4. Before connecting your computer to the internet, install the anti-virus and anti-spyware programs. I have Symantec anti-virus and Spybot Search and Destroy. They seem to work pretty well. If you're really paranoid, get something like ZoneAlarm firewall as well.
5. Now that you have security software installed, it is safer (not safe, but safer than with no protection) to get on the Internet. In Internet Explorer, there is only one site you should visit: http://www.mozilla.com/en-US/ Get Firefox, use it for all your web browsing. If you find you don't like it much, then use it to download other browsers like Opera, Safari, Seamonkey, or Chrome.
6. Delete Internet Explorer, or at least eliminate all icons for it from your quick-launch bar, desktop, and menus. Yes, I am serious. I went out of my way to make IE completely inaccessible when I installed Vista. Running it is like having a giant "data-mine me" sign on your computer.
7. Be sure to turn off all the gaping security holes such as file-sharing.
8. If you want a more secure system, switch to an open-source *nix system like Linux (Ubuntu is n00b-friendly) or BSD. You can still run all your Windows programs under Virtualbox and/or Wine if you want to. The main thing you'll lose is gaming. If you want to stick with Windows, fine, but know that it is much more of a challenge to keep Windows secure than it is to find the correct wireless driver in Linux.
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WAR IS PEACE
FREEDOM IS SLAVERY
IGNORANCE IS STRENGTH