Official firmware 1.50 update EBOOT for PSP, primarily used as a helper file with HEN, a homebrew enabler capable of downgrading a PSP to 1.50 under the right conditions. In the past, it has also been essential to the installation of custom firmware.
Firmware 1.50 was the first publicly available firmware update, initially released over Network Update for Japanese launch units running 1.00.
The 1.50 firmware by itself supports homebrew out-of-the-box, thanks to a security vulnerability found by hackers in late 2005. Sony quickly patched this hole with the release of firmware 1.51.