We love our Macs. We especially love them because they don’t get attacked by malicious viruses… for the most part.

The security of approximately 600,000 Macs has been compromised by the Flashback trojan, a trojan that targets an unpatched Java vulnerability within Mac OS X. The Mac Trojan horse was first detected in September, 2011. Hackers continued to adjust the malicious software to include both social engineering tricks and exploits of vulnerabilities.

Hackers started spreading the BackDoor.Flashback.39 Trojan horse approximately four weeks ago. This time it exploited a Java vulnerability that was unpatched on OS X. Dr. Web, which sells an antidote for the versions of Flashback on Microsoft machines describes the Mac Variant:

JavaScript code is used to load a Java-applet containing an exploit… The exploit saves an executable file onto the hard drive of the infected Mac machine. The file is used to download malicious payload from a remote server and to launch it…It may get and run any executable specified in a directive received from a server.

Oracle released an update that closed the hole in February. Apple didn’t fix the vulnerability until earlier this week after the news began to spread according to Ars Technica‘s Jacqui Cheng.

According to Russian malware analyst Ivan Sorokin, over 600,000 Macs have been affected. That number includes 274 machines “from Cupertino” also known as Apple’s headquarters. Tha

Rest assured, the fix is found in the OS X software update Java for OS X 2012-001. Look for it in the software update in system preferences. Also, a firm called F-Secure has instructions on how you can find out if your Mac is infected by the Flashback trojan. Please note that the instructions do involve running commands in Terminal so you should follow the instructions exactly as you read them.