If your having poroblems installing Bitdefender Anti Virus on Windows 10 technical preview, try this (works for me).

Download the Bitdefender installer from Bitdefender website. If you bought it online then use the link in your purchase email.

Place the file somewhere easy to get to, like c:\temp.

Now use the compression program of your choice to unpack the contents of the file. I use 7-zip, so right click the downloaded file and select ‘7-zip’ -> ‘Extract to’.

now open a command prompt as administrator and navigate to c:\temp

cd c:\temp
setupdownloader.exe /silent


The install is silent, there will be no on-screen progress or results. Just wait a minute or two (depending on your internet speed) while the program downloads and installs. Eventually you will see the Bitdefender program appear in the system tray.

Enjoy

Having trouble getting Windows Defender to start. Maybe you just removed an ant virus program and now you are getting messages like ‘This app has been disabled’.

Try opening a command prompt as administrator (right click->select ‘Run as Administrator’) and type

sc start WinDefend Enable

One reboot later and you should be good to go.