The remote Mac OS X host appears to have been compromised.
Using the supplied credentials, Nessus has found evidence that the remote Mac OS X host has been compromised by a trojan in the OSX/Flashback family of trojans. The software is typically installed by means of a malicious Java applet or Flash Player installer. Depending on the variant, the trojan may disable antivirus, inject a binary into every application launched by the user, or modifies the contents of certain web pages based on configuration information retrieved from a remote server.
Restore the system from a known set of good backups.