A new variant of the Gozi Trojan has been discovered, raising the specter of a comeback for the infamous malware, which excels at pilfering financial information even when it's protected using supposedly secure mechanisms.

The new strain was first detected on Tuesday when Russian miscreants unleashed a small avalanche of malware-tainted PDF files (http://www.theregister.com/2007/10/24/pdf_exploit_in_the_wild/) that tried to remotely hijack vulnerable computers. Don Jackson, a researcher with security provider SecureWorks, said the exploit turned Adobe's PDF Reader program into a malware installer that loaded the new Gozi Trojan onto victims' machines.

Jackson's discovery is yet another powerful reason for users to update Reader (http://www.adobe.com/support/downloads/detail.jsp?ftpID=3806) and Acrobat (http://www.adobe.com/support/downloads/product.jsp?product=1&platform=Windows) immediately. Otherwise, he says, users are wide open to a Trojan that thieves have used to steal more than $2m worth of financial and personal data already.

"People aren't going to block PDFs," he told El Reg. "There's just too much business done to block it all. And what happens when you start using PDF-type books?"

Only 26 per cent of the major antivirus providers protect against the new variant, he said. It is detected under names including OrderGun, Orderjack, Germ, Small.BS, Pinch, Snifula, Ursnif and CWS.

Jackson first sounded the alarm on Gozi (http://www.secureworks.com/research/threats/gozi/?threat=gozi) in March. The program uses Winsock2, advanced functionality that allows it to snoop on traffic even when it is protected in Secure Socket Layer sessions. It also uses customized server/database code to collect sensitive data.

Tuesday's PDF exploit comes to us courtesy of the Hang Up Team, Jackson says. While the Russian crime gang may exhibit evil genius in writing code, the group is considerably more amateurish when it comes to spam. As a result Tuesday's attack was relatively easy for most spam filter services to block.

"Spam is not their forte," Jackson said. "If they contracted a spam service to send it out, it would have been a lot more successful." ®

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