Watch Out for Trojans Circulating in PDFs

Websense Security Labs has received several reports of a Zbot trojan campaign spreading via email that connects your PC to a malicious remote server in China. They have seen over 2,200 messages so far.

Zbot (also known as Zeus) is an information stealing trojan (infostealer) collecting confidential data from each infected computer. The main vector for spreading Zbot is a spam campaign where recipients are tricked into opening infected attachments on their computer.

This new variant uses a malicious PDF file which contains the threat as an embedded file. When recipients open the PDF, it asks to save a PDF file called Royal_Mail_Delivery_Notice.pdf. The user assumes that the file is just a PDF, and therefore safe to store on the local computer. The file, however, is really a Windows executable. The malicious PDF launches the dropped file, taking control of the computer. At the time of writing, this file has a 20 perecnt anti-virus detection rate (SHA1 : f1ff07104b7c6a08e06bededd57789e776098b1f).

Location of the Zbot:

The Zbot trojan creates a subdirectory under %SYSTEM32% with the name "lowsec" and drops the "local.ds" and "user.ds" files. The "local.ds" and "user.ds"  are configuration files for the threat. It also drops an executable "sdra64.exe" and modifies the registry entry "%SOFTWARE%\Microsoft\WindowsNT\CurrentVersion\Winlogon\Userinit" to launch itself during system startup. When it runs, it injects malicious code into the Winlogon.exe instance in memory. This Zbot variant connects to malicious remote sever in China using an IP address of 59.44.[removed].[removed]:6010.

This is yet another hacking attempt pointing to China, which is kinda alarming and makes one wonder if China is quietly planning to go big on this. Make sure you've updated your anti-virus suites with latest definitions in order to keep your PC from malicious data. Also, avoid downloading any PDF from unknown senders.