The Norton Antivirus family detects Actions Server as an unknown but possible virus and, depending on your security settings, it automatically erases the file.
This is called a "false detection", it sometimes happens with antiviruses, and it is already happened several times to other developers.
We sent out a “false detection report” to Norton so they will be able to correct it in their virus database.
While we wait for Symantec to correct this false detection you need to temporary disable Norton security before to download our installer, and keep the antivirus disabed until you complete the installation.
Try right clicking on the Norton icon in your notification area. You should be able to disable protection features for a specified time. Remember that you are unprotected while doing this, so you should reset the protection on when you have finished.
We will post in all our channels an update as soon as we receive confirmation from Symantec that the issue is fixed.
the Usefool team