Flashback botnet decline not as fast as expected

Given the attention that the Flashback Mac malware has received since the discovery of the 600K strong botnet of computers infected with it and the number of tools that various security firms and Apple issued for its removal, it’s somewhat disheartening to hear that the botnet still counts around 140,000 zombies.

“We had originally believed that we would have seen a greater decline in infections at this point in time, but this has proven not to be the case,” commented the Symantec researchers who have set up a sinkhole to monitor the botnet’s existence but offered no explanation for the unexpected slow decline.

The researchers say that the domains hosting the C&C server for the botnet change every day, and that they are not limited to the .com domain, but will also be set up on .in, .info, .kz and .net top level domains.

They also point out that among the new features of the Trojan is the ability to “retrieve updated C&C locations through Twitter posts by searching for specific hashtags generated by the OSX.Flashback.K hashtag algorithm.”

Users who haven’t yet installed the latest Java update (for OS X Lion and OS X Snow Leopard) are advised to do so because the Java vulnerability (CVE-2012-0507) misused by Flashback is currently being exploited to install another Mac Trojan called SabPub, and others can crop up at any time.