Some parts of the source code has been released to the public for more than 2 years. It includes the missions, some global AI, characters and maps. But the most interesitng parts, like the weapon system and AI is not available. The new executable has been made by hex hacking the e6.exe, those Russkies certainly know what they're doing
If you're intersted in the released source code, let me know and I'll post a link to it.