There is a reason for there are no modding tools available for Battlefield 3—DICE is worried that they would leave the game vulnerable to hacks and exploits.
Although it was aware of what mods could do for a game’s longevity, DICE was "afraid of all the things that can come with releasing the code," said GM Karl Magnus Troedsson.
He also stated that his company wanted such tools to be available on console as well as PC, something that was substantially trickier to implement.
"If we do mod support, we want to do it really, really well." he said.
"We are not ready to do this yet."
Official modding tools were available for the game’s prequel, Battlefield 2.