Windows Update is the best way to keep your computer from becoming vulnerable to security risks.
If your using Windows 7, Click Start and Control Panel
Click System And Security
Click Turn automatic updating on or off
Make sure that Install updates automatically is selected.
Then choose a time to install the updates and click OK
If your using Vista, Click Start and Control Panel
Under Windows Update click Turn Automatic Updating On or Off
In this window you can choose a date and time that best suits you and click Ok