To check if you are infected with the BackDoor.Flashback.39 trojan you can use a simple free utility created by jils.
The utility can be downloaded from here. Simply run the application and click the Check for Flashback Infection button.
Over 600,000 Macs are said to have been infected with the trojan. Make sure to run Software Update and install the latest Java security patch which will close the exploit.
Read More [via Rick]