Code writers behind the latest Citadel trojan, dubbed the "Rain Edition," have added advanced features and significantly boosted the price tag of the malware.

The new iteration includes a feature, called "Dynamic Config," which allows botmasters easier access to compromised victims' machines by updating the malware's configuration file immediately. Configuration files are used by owners of command-and-control servers to communicate malicious instructions to hacked PCs under their control.

The first version of Citadel, a variant of banking trojan Zeus, entered the black market in January at cost of $2,399, but now commands a fee that is 41 percent higher – $3,391 for the latest, or sixth, Citadel release.  

Limor Kessem, technical lead and fraud expert at RSA, told on Thrusday that the “dynamic config” feature exemplifies just how advanced Citadel programmers are. RSA published a blog post Thursday divulging the details of the latest software released by the malware's authors.

“They are able to implement changes that come directly from the command-and-control server in real time,” Kessem said of the newest feature. “They are cutting out time and the need [for developers] to change the whole configuration file. They can correspond immediately with a victim who is sitting in front of a screen. It's really a breakthrough. We've never seen them do that.”

Citadel, along with other banking trojans, usually infects users through spam or drive-by download campaigns launched by saboteurs. Banking malware often aims to steal account login credentials to transfer money to attackers, either in the background or by hijacking victims' computers.