How does Flashback Malware get into a Mac?

If your Java is not updated, it uses two exploits to get in.

If your Java is updated it tries a social exploit by various windows like Flash update or Software Update to trick the user into providing their password.

However if it see's LittleSnitch it will delete itself.

Best action is to (10.6 and later) Software Update (cleans it off and fixes Java) and then turn off Java in your web browser preferences, if you have Java installed, which new Mac's don't.

Also read some info here

Harden your Mac against web attacks

 Most commonly used backup methods explained

https://discussions.apple.com/community/notebooks/macbook_pro?view=documents

My understanding is that for "Flashback-K", the recent variant that caused the most widespread infection, by the time you see a "Trojan-like" screen that asks for your password the Flashback files have already been installed into your system, and the malware is only choosing which method to use to try complete the infection.

The detailed description of Flashback-K here indicates that only way that this particular infection gets initiated is by browsing to an infectious website from a system that has a non-updated version of Java installed and also enabled in the browser. This initial "dropper" phase is a "drive-by download" - there is no popup screen displayed, and nothing to click on. It is therefore not a true "Trojan" at this stage - if you have a vulnerable version of Java enabled you cannot prevent the infection by being "careful" regarding clicking on links or giving your password. Nor can avoiding "questionable" websites prevent an infection - the infectious websites themselves can be perfectly legitimate sites that have been hacked and the malware planted there.

After the initial files are dropped via the Java exploit, they download more files from a remote server, and only then are you offered a fake but authentic-looking popup message that asks for your admin password. At this point you are already infected - if you give the password the infection tries to proceed in a more targeted and stealthy manner, directly modifying your browser. If you don't give your password, you end up with a user-specific infection that can affect more applications and therefore be more easily noticeable.

The ‘Flashback Trojan’:

A version of an existing Trojan Horse posing as a legitimate Flash Player installer (named “Flashback.A” by a security firm) is designed to disable updates to the default Mac OS X anti-malware protection system, potentially leaving the system open to the manual installation of other malware without any system warnings. The most recent versions bypass any user action and automatically installs itself after an affected website is visited.

http://www.appleinsider.com/articles/11/10/19/fake_adobe_flash_malware_seeks_to_ disable_mac_os_x_anti_malware_protection.html

(Adobe is aware of malware posing as its Flash Player and warns users to ignore any updates that didn't originate on its own servers. "Do not download Flash Player from a site other than adobe.com," said David Lenoe, Adobe's product security program manager, in an entry on Adobe Product Security Incident Response Team's PSIRT blog. "This goes for any piece of software (Reader, Windows Media Player, QuickTime, etc). If you get a notice to update, it's not a bad idea to go directly to the site of the software vendor and download the update directly from the source. If the download is from an unfamiliar URL or an IP address, you should be suspicious.")

Flashback Trojan - Prevention of infection:

In order to prevent a potential infection with “Flashback” Trojans, Mac users should always obtain their copy of Adobe Flash Player directly from Adobe’s official website and to disable the "Open 'safe' files after downloading" option in Safari Preferences/General to avoid automatically running files downloaded from the Internet. Also, do not turn on Java in Safari Preferences/Security. Few websites use Java. Javascript is something entirely different and should be left active.

The Flashback Trojan does not affect PPC (non-Intel) Macs, nor has it been noted to affect users running Tiger OS 10.4.11 or Leopard OS 10.5.8.

Last, but by no means least, using Open DNS is the simplest way of preventing infection in the first place. Open DNS also protects against phishing attacks, re-directs, speeds up your internet connection, and works for all users of OS X from Tiger upwards:

http://blog.opendns.com/2012/04/09/worried-about-mac-malware-just-set-up-opendns /

How to get it:

https://store.opendns.com/get/home-free

Flashback Trojan - Detection and Removal

Users with Intel Macs running Snow Leopard OS 10.6 or Lion OS 10.7 should ensure that they have downloaded all the recent Java updates from Apple, which are designed to prevent infection and also remove any infection already present.

New Macs running Lion do not have either Flash Player nor Java installed. If you running Lion and have not already downloaded and installed Java, you should download the ‘Flashback malware removal tool’ from Apple: http://support.apple.com/kb/HT5246 (356KB) which includes the same code as the Java update that plugged a security hole which allowed the malware to automatically install itself without admin authorization.

You can also use this to check whether you have been infected (for Intel Macs only) and remove it if required:

http://www.macupdate.com/app/mac/42571/anti-flashback-trojan

Flashback Trojan - Detection, and how to remove (with caution) if you are running other browsers than Safari:

http://www.f-secure.com/v-descs/trojan-downloader_osx_flashback_i.shtml