When news broke that Verizon's and AT&T's versions of the Galaxy S4 would ship with locked/non-unlockable bootloaders, people were... upset. This sort of action was basically expected from Verizon, but AT&T had historically left its device's bootloaders unlocked, allowing users to do what they wanted with their own handsets. To make matters worse, the Galaxy S4's bootloader signature verification is nearly impossible to crack.
Then, at the first of the month, all-around genius hacker Dan Rosenberg released a teaser for his upcoming tool that would "hack" the AT&T's versions bootloader. That tool, now knows as Loki, is finally available for download, and it also works on Verizon's version of the device.