Two weeks ago, Mac security researchers at Intego discovered a variant of the Flashback Trojan using clever methods to infect systems. On Friday, Intego reported that a new variant of Flashback is targeting passwords and as a byproduct of infection, Flashback is crashing several notable applications.

Flashback was first discovered by Intego in September of 2011. It targets Java vulnerabilities on OS X, two of them to be exact, in order to infect the system. Should Flashback find that Java is fully updated, it will attempt to social engineer the malware’s installation, by presenting an applet with a self-signed certificate. The certificate claims to be signed by Apple, but is clearly marked as invalid. However, users are known to skip such warnings, thus allowing the malware to be installed.

“Since Mac OS X 10.7 Lion, Java is no longer included with the operating system...While most users may not use any Java applets, it is fairly common for online meeting and collaboration services to use Java, as it is cross-platform. Because of this, many Mac users may not realize that they have Java installed, as they may not remember having downloaded it when presented with such a request,” Intego explains.

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On Friday, Intego discovered a new variant of Flashback, and noticed several examples of it infecting systems, thanks to users who posted details on various public forums after noticing application crashes. The newest variant will render programs such as Safari and Skype unstable, causing them to crash. Interestingly enough, normally these are stable programs, so if they start suddenly crashing might be a sign of larger issues.

“Flashback.G injects code into web browsers and other applications that access a network, and in many cases causes them to crash. It installs itself in an invisible file in the /Users/Shared folder, and this file can bear many names, but with a .so extension,” Intego noted.

“This malware patches web browsers and network applications essentially to search for user names and passwords. It looks for a number of domains – websites such as Google, Yahoo!, CNN; bank websites; PayPal; and many others.”

If Java isn’t needed delete it, or at least keep it updated. It’s also wise to look for and refuse installations if presented with a self-signed applet certificate that’s reported as untrusted. The latest variant of Flashback also comes with a failsafe, as it will not install on systems running Intego’s security suite.

As mentioned, users running OS X 10.6 (Snow Leopard) are the targets, as Lion does not initially come with Java installed.