Microsoft released a number of security updates for the 8.1 preview, namely:



Windows Store app instability after an app update in Windows 8.1 Preview




Internet Explorer 11 Preview freezes or crashes while loading a webpage that contains widgets




Smart card PIN disclosure after an automatic restart for Windows Update in Windows 8.1 Preview




No notification about the expiration date of Windows 8.1 Preview

These updates should appear via the windows update utility