The number of Mac OS infected by the Flashback malware is slowly dwindling down as Symantec reported that from 600k infections from April 9, it’s now down to 140,000.
The OSX.Flashback.K is a trojan that works as social-engineering scam trying to pass off as a fake Flash update using digital certificates purporting to come from Apple. It uses a domain name generator (DNG) algorithm that allows it to generate a new domain each day in order to contact the command-and-control (C&C) server to keep the distribution going.
What sets this threat apart from typical Mac Trojans is the sheer size of Mac computers that have been infected, with initial estimates ranging in the region of 550,000. As there have been tools released by Symantec and other vendors in the past few days concerning this threat, the infection numbers should have seen a dramatic decrease by now.
If you suspect that your Mac has been infected with OSX.Flashback.K, it is recommended to install the latest patches, ensure that your antivirus is up to date with the latest signatures, and to use the free Norton Flashback Detection and Removal Tool.[Symantec Blog]