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
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.