Back to my Mac secure?
From Apple's website:


  Back to My Mac uses these methods to protect your security:
  
  
  IPSec and SSL encrypt and secure communication between your Macs and the Back to My Mac servers. Anything you transfer between Macs is
  protected.
  Kerberos with digital certificates provide secure and trusted authentication to help verify identity. An added benefit: with
  Kerberos, you won’t have to enter your user name and password every
  time you connect to another Mac in your Back to My Mac network.
  
  
  You can make your network even more secure by changing a few optional
  settings.