Security researchers shed new light on Duqu, a worm that is believed related to Stuxnet. Russian IT security researcher characterizes the developers of Duqu as “a rather professional team of developers” Researchers studied a component of a new version of the worm that it says was compiled on Feb. 23. Duqu was compiled with a 2008 version of a Microsoft Visual Compiler using special options known as /O1 and /Ob1, most likely written with a custom extension to C called OO C.”]
Source: https://www.bankinfosecurity.com/experts-shed-new-light-on-stuxnet-kin-a-4618