Firmware 11.4 actually patches the exploit, which is what triggered the release: Smealum had implied the release would happen once the exploit gets patched.
The exploit, nicknamed Udsploit, allows 3DS users to fully hack their 3DS, with all bells and whistles (although downgrading might be out of the picture). According to the readme, the exploit was found by yellows8, and the full weaponized code is by Smealum.
People looking to get their 3DS hacked should not update to the recently released firmware 11.4. Those of you who want to enjoy one of Nintendo’s legendary “stability updates”, however…
Download and install udsploit
At the moment, no binary has been released, but the exploit’s source code can be downloaded from the developer’s github here. People with the right sets of skills will probably soon distribute more “user friendly” versions. Stay tuned.