Mangham's copy of the source code would surely have been of interest to cybercriminals who attempt to use Facebook to perpetuate scams. But he wrote he had no intention of selling the code.

"It is also worth mentioning that I had the source code for just over three weeks with absolutely nothing to prevent me from making copies and redistributing it, this was more than enough time to have caused significant damage to Facebook or to find a buyer, if that had ever actually been my intention but quite clearly it was not," Mangham wrote.

"When you consider that the only thing that stood between Facebook and potential annihilation were my ethics then I think the fact that it's all still in good working order should serve as some proof that I'm really not one of the bad guys," he wrote.