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How secure is an encrypted Linux file system contained in a VirtualBox virtual drive on a Windows host?

I'm looking for any information regarding how secure an encrypted Linux file system is when contained in a VirtualBox virtual drive on a Windows host? Specifically I'm looking for answers to the following questions:

  1. Does the fact it is hosted as a guest system expose the encrypted data to any new attack vectors?
  2. Aside from the threat of key loggers on the Host OS, malware etc., when the virtual machine is turned on is there the threat of a rogue host process accessing the virtual machine's file system on the fly?
  3. When both the Host and Guest OSes are turned off and the data is at rest on a storage device, is it any easier/harder to retrieve the encrypted file system?