In the advertising business, they say you have to be crazy not to be paranoid!
You can say the same for using computers. Windows is a minefield. You must have antivirus software. (I use Microsoft Security Essentials.) But even more important than that--you have to update Windows regularly. Microsoft issues monthly security updates. But to get those updates, you either have to have Automatic Updates set up to receive them, or you have to manually update Windows yourself.
Go to Start, Control Panel, and double click on Security Center. See if Automatic Updates are set to load. That is Windows' recommended setting.
Now hear this—Don't listen to them. Don't let them take charge. For your own safety, you should control what Microsoft is installing. If you are comfortable tweaking your system, here's what to do: Change the setting from automatic downloads and set it to only notify you that you have updates ready to be installed. This is not the place for a detailed discussion, but these updates can sometimes cause more problems that they solve.
Windows Wizard Woody Leonhard has just declared it safe to update. Go for it now. Read MS-DEFCON 4: Patch everything except the Office 2010 Service Pack @ AskWoody.com
For more information on Windows updates see Automatic Updates. For more information on Woody's Microsoft patch defense system see MS-DEFCON System
If all this is Geek to you, just leave your machine on automatic updates. And pray. In fact, pray anyway. It never hurts.