The latest upgrade (on the windows side) is a piece of work (POS, in other words) as upgrading, was a bear.
If it fails to upgrade and you get the odd (MSI not found error) when upgrading from r16 to r18, here's a fix that may work for you (did for me):
(Stolen from https://forums.virtualbox.org/viewtopic.php?f=6&t=45536&sid=a10eb1d37e85adc7b814470463b4b314&start=15)
After trying everything and having made sure that all certificates were in order and that all drivers could be installed perfectly fine, I finally found a solution for this problem that worked for me. It had nothing to do with the driver certificates, and all to do with the driver verification done by the installer.
To install VirtualBox with that error, do the following:
- Download the Orca MSI editor. http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&sqi=2&ved=0CFUQFjAA&url=http%3A%2F%2Fwww.technipages.com%2Fdownload-orca-msi-editor.html&ei=zxcIUIuiFePs2QWWm5DeBA&usg=AFQjCNGXxLvTAxxEIQiKhNrV3gWCn_paVg
- Start "cmd.exe" via the Start->Run and navigate to the directory you put your setup.exe.
- Execute "VirtualBox-4.1.16-78094-Win.exe -x"; adjust this to whatever version of Virtualbox you wish to install.
- The installer will tell you where it has extracted the files to. Go there and move them somewhere more accessible.
- Start Orca
- Open the MSI file for your platform that you've just extracted & copied. In my case this is "VirtualBox-4.1.16-r78094-MultiArch_amd64.msi"
- Enter the table "InstallExecuteSequence"
- Drop the row "MsiProcessDrivers"
- Save the MSI file.
- Verify that the MSI file's modified-date has changed (for some reason Orca sometimes does not save the file)
- Run the changed MSI.
After that, the install should work perfectly fine and ask you whether you really do want to install the drivers, even though they're not WHQL certified. Say yes to them all and enjoy using VirtualBox.
Orca MSI Editor: