Zero-day exploits hit vulnerabilities in a program that the software's maker has not had time to patch yet. But even during this time of exposure, you have ways to help keep your computer safe.
1. Get rid of Internet Explorer 6. One of the best moves you can make to improve Internet safety is to ditch Microsoft's notoriously hole-infested browser. No program is completely safe, of course; but whether because it is inherently vulnerable or because its massive user base makes it an attractive target, IE 6 might as well have a giant bull's-eye painted on it. Upgrade to IE 7 or to an alternative browser such as Firefox or Opera.
2. Try alternatives to other programs that have been targeted by zero-day attacks. The free Foxit program displays PDFs, for instance, and OpenOffice works with many Office documents.
3. Enable automatic updates for Windows and other programs whenever possible. Patches won't help against zero-day incursions, but major vulnerabilities tend to remain targets even after the fixes are released, precisely because attackers know that many people don't bother patching. To check and change your Windows Update settings, click Automatic Updates in the Control Panel. To keep up with the changes to your system, we recommend choosing Download updates for me, but let me choose when to install them.
Other programs make it more or less easy to find automatic-update settings. For example, in Firefox, head to Tools, Options, Advanced, and select the Update tab (again, we recommend selecting Ask me what I want to do as the standard course of action when Firefox finds updates). To find the settings in Adobe Reader, you'll need to check manually for updates under the Help menu, and then click the Preferences button.