The antivirus software (Kaspersky) I had installed before going through the 8.1 Preview installation doesn't seem to be working now. Will I be alright just using Windows Defender, or should I install something else? If so, what should I install?

I think Windows Defender is good enough for most scenarions where you not need to control the antivirus software.

It is usually best to uninstall security software prior to an in-place upgrade.

Windows Defender will be effective for the 8.1 Preview test.

Do you understand that you will not be able to go to the RTM 8.1 from the preview?

It is usually best to uninstall security software prior to an in-place upgrade.

Windows Defender will be effective for the 8.1 Preview test.

Do you understand that you will not be able to go to the RTM 8.1 from the preview?

According to the Windows team on their blog, you will be able to upgrade from Preview to RTM, but you will not be able to keep all your apps, just data.

Thank you Sergio, for the clarification. I interpret that as I cannot upgrade, because of all of the time it would take to re-install and configure all of the desktop applications.

One can save all of their STORE apps to SkyDrive file back and then restore them.

Whatever works for the user.

Here is the excerpt from the blog:

"Its also important to note that while computers running Windows 8.1 Preview can be updated to the final Windows 8.1 release, this update process will only migrate the data on the device. All applications (from the Windows Store or desktop applications) will need to be reinstalled as part of this process. To illustrate:

If you are currently running	Going to	This will migrate:
Windows 8	Windows 8.1 Preview	All data, settings, and applications
Windows 8	Windows 8.1 final release	All data, settings, and applications
Windows 8.1 Preview	Windows 8.1 final release	Only data