According to iClarified, Apple has updated the BootROM for the iPhone 3GS to iBoot-359.32. This software upgrade is reportedly not vulnerable to an exploit hackers previously used to crack open the hardware.
A member of the iPhone Dev Team who goes by the handle MuscleNerd noted this is the first time ever that Apple has done a BootROM update in the middle of a product line, without a new hardware model. The Dev Team is a group of hackers who release tools used to exploit the iPhone OS.
Previously, hackers had relied on an exploit known as "24kpwn," which allowed users to run unauthorized code on the iPhone OS. The latest BootROM, however, does not allow use of the exploit.
Apple's interest in preventing users from jailbreaking, or running unauthorized code, on their iPhone is likely centered around piracy. While jailbreaking does have other uses than piracy — such as running applications not allowed on the App Store or unlocking the device for use on other carriers — the procedure can also allow users to steal software from the App Store.
Apple and the jailbreaking community have gone back and forth for some time, as the handset maker looks to close avenues used by hackers.