McAfee, via Help Net Security, have reported that they have seen cross-platform malware in the form of a Java Trojan they have named IcognitoRAT, which targets and attacks both Windows and Mac OS users.
The Trojan is installed by another component, and was originally created as a Windows exploit, using the JarToExe utility.
Once the .jar file is converted, it is executed and downloads a number of Java-based utilities, which in turn are executed, and turns the system into part of a botnet, which the botnet herder is able to use to control the mouse, keyboard and any camera that may be installed. Any information stolen is sent to a predefined email account.
Although informational sources on the botnet underground suggest the malware can be used on both Windows and Mac (with control software available for iPhone / iPad as well), currently the in-the-wild version has only been seen working on the Windows platform.