Apple Remote Desktop before 3.6.1 does not recognize the "Encrypt all network data" setting during connections to third-party VNC servers, which allows remote attackers to obtain cleartext VNC session content by sniffing the network.
http://www.securityfocus.com/bid/55100
http://support.apple.com/kb/HT5433
http://lists.apple.com/archives/security-announce/2012/Aug/msg00000.html