Downloaded the 8.0.1492 beta for avast_free_antivirus_setup.exe, turned off Windows Defender in Windows 8.1 Preview and installed. The install went fine without the compatibility issues that occurred with the latest release version of 8.0.1489. Then a train wreck.... Compatibility screens began to show, to which I choose to "run the program anyway". I was then greeted with about 100 memory error screens. I tried to gracefully shut the computer down, but more memory error screens were shown. Finally, I did a hard shutdown by holding down the power button for four seconds. Restarted Windows 8.1 Preview in safe mode. Ran aswclear.exe and restarted computer. As far as I can tell, Windows Defender and Norton are the only two antivirus programs that will run with Windows 8.1 Preview at this time. I have tried eset Nod32 and while it installs it also has errors. I am currently using Norton Antivirus 21 beta, which has played nice with Windows 8.1 Preview so far. The beta subscription is only good for 14 days.