The GSG shroud was recalled in 2010 because it was simple to convert to a suppressor...not by modifying the shroud but porting the barrel itself.

To explain a bit. The GSG shroud threads at the base of the hand guard apposed to the front like most shrouds on the market. Being threaded at the base meant the barrel passed through a hollow tube (the shroud) and sealed at the back by the hand guard where its threaded. People were drilling/porting there barrels hence making it a suppressor..kinda like an integral suppressor to be exact. The new GSG shroud still threads at the base but has an additional internal tube running through it about .050 bigger then the barrel diameter itself. This is all welded together so the internal tube in the shroud can not be removed.

*Again it would be easier to go to home depot to build a suppressor from scratch then it would be to convert any shroud into one. Of course not condoning this do to legal reasons just trying to make the point. Hell the ATF will tell you a water bottle is a suppressor if you ask. So if you have a gun, bottle of water and some tape all in you car a the same time.....look out don't get caught.