For all of the concern around Duqu, the most discussed piece of malicious software since Stuxnet, the latest analysis of its code shows its writers have a sense of humour.
Wrapped in the code used to infect computers is an "Easter egg," or a hidden message. Easter eggs have long been inserted in computer code, often seen only by those who enjoy browsing computer code.
Duqu's exploit, the code used to take advantage of a software vulnerability, contained the line: "Copyright (c) 2003 Showtime Inc. All rights reserved. DexterRegularDexter."
The reference to the television show "Dexter" is meant as a joke. The shellcode of the exploit is contained in an embedded font called "DexterRegularDexter," which is processed by Windows' Win32k TrueType font parsing engine, wrote Aleks Gostev, a senior analyst with the Global Research and Analysis Team for Kaspersky Lab.
"This is another prank pulled by the Duqu authors," he wrote.
There actually is no font called Dexter, though, and it is just a name the malware authors assigned to the file, said Costin Raiu, director of Kaspersky's Global Research and Analysis Team.
Kaspersky and many other computer security companies have been analyzing Duqu since it surfaced. Duqu shares some similarities with Stuxnet, the malware believed to have been created with the intention of disrupting Iran's nuclear programme by tampering with centrifuges used to enrich uranium. But experts remain uncertain if there is a connection between the developers of the two pieces of malware.
Gostev's latest write up is an analysis of a version of Duqu that came from Sudan's CERT (Computer Emergency Response Team), which had a sample of Duqu from an unnamed organisation that was infected.
Victims are infected by an exploit delivered via a tampered Microsoft Word document, which, if opened, delivers Duqu. Gostev's post includes a screenshot of the simple email purporting to come from a marketing manager, "Mr. B. Jason," requesting that the receiver open a Word document and answer a few questions such as "Do you supply marine shipping?"
Other clues in the code have indicated that Duqu could be as much as 4 years old. A driver loaded by Duqu's exploit into the Windows kernel has a date saying it was compiled on Aug. 31, 2007, Gostev wrote. But that may not be accurate, since Duqu has different components that could have been created at different times.
Another oddity discovered by Kaspersky is how often attacks occurred on Wednesdays.
"The Duqu gang has an affinity for Wednesdays,"Raiu said. "They have repeatedly attempted to steal information from these systems on Wednesdays. This probably indicates a strong routine, almost military type."
The attackers also took a lot of care when they struck to avoid being detected. They used separate command-and-control servers for each unique set of files. They also crafted a unique Word file for each victim and sent the malicious files from anonymous e-mail accounts, probably on compromised computers, Gostev wrote. They even modified the shellcode for different attacks.
The evidence points to a high level of sophistication. "The exploit used to infect victims with Duqu is incredibly well written, beautiful in a sense," Raiu said. "The Duqu authors are top-class exploit writers."