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
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