Researchers around the world put their heads together and solved the identity of mystery code in the Duqu Trojan horse program, researchers from Kaspersky Lab announced on Monday. The mystery code was written in the common C programming language and compiled with Microsoft Visual Studio 2008. The Duqu authors modified the underlying C code with a customized extension for combining object oriented programming with the older C language a variant sometimes termed OO C The use of OOC rather than the more common C++ language suggested that the developers who wrote Duqu were likely older developers.
Source: https://threatpost.com/duqu-s-mystery-code-not-new-just-old-school-031912/76341/