There is an interesting PowerPoint presentation you can find on the internet on how Skype used to evade debuggers. http://www.secdev.org/conf/skype_BHEU06.hand

There is an interesting PowerPoint presentation you can find on the internet on how Skype used to evade debuggers. http://www.secdev.org/conf/skype_BHEU06.handout.pdf http://www.secdev.org/conf/skype_BHEU06.handout.pdf The techniques described in that document are different, but in a way they are alike - both use dirty tricks to shield themselves from people trying to reverse engineer them. The only difference is that one takes place "at compile time", in way, while the other works in a dynamic program as it is executing.