Security Experts:

Shylock Trojan Now Can Spread Through Skype

The Shylock banking Trojan has been updated with new capabilities that allow the malware to spread and infect users over Skype.

The malware's new Skype functionality appears to have been added earlier this week, according to security researchers from Danish IT security firm CSIS Security Group. The new plug-in allows the malware to send rogue messages and files using the Skype VoIP and instant messaging client installed on the infected device, Peter Kruse, CSIS partner and security specialist, wrote on the company blog. The malware is also able to bypass Skype warnings messages and delete traces of its activity from Skype history, Kruse wrote.

Previously, Shylock used MSN Messenger, Yahoo Messenger and other real-time chat programs to spread. Infected users were inadvertently sending the malware to their contacts via instant message. Users were tricked into clicking on a link in the message which directed them to a site hosting the malware.

Shylock's creators may have decided to add Skype to its list of distribution methods because Microsoft announced plans to retire Messenger in March and move all the users to start using Skype, Kruse said. "Shylock is one of the most advanced Trojan-banker [malware] currently being used in attacks against home banking systems," Kruse said. "The code is constantly being updated and new features are added regularly."

Along with stealing login credentials for online banking services, Shylock has a number of other capabilities. Cyber-criminals have access to the cookies stored on the infected computer and the malware installs VNC remote control software to give the controls the ability to take over the machine. Shylock can also manipulate websites within the browser by injecting text and transferring files to a remote server.

SecurityWeek has reported on previous updates to Shylock, such as the new feature which can detect whether the malware is being installed on a machine using the remote desktop protocol.

CSIS believes the bulk of victims are from the United Kingdom, although there were many infected computers throughout mainland Europe and the United States.

"Shylock is active in only a few parts of the world," Kruse said.

Fahmida Y. Rashid is a contributing writer for SecurityWeek. She has experience writing and reviewing security, core Internet infrastructure, open source, networking, and storage. Before setting out her journalism shingle, she spent nine years as a help-desk technician, software and Web application developer, network administrator, and technology consultant.