Sony pulled two PSP titles, Hot Shots Tennis and MotorStorm Arctic Rift, from the PlayStation Network in March when they were found to be open portals to Vita hacking heaven, allowing people to use homebrew programming through the Vita's PSP emulator. Both of these titles are currently back on the Vita and the hack scare is gone forever and ev – er, maybe not.
Vita version 1.67 closed off the ability for hackers to run the VHBL program in Hot Shot Tennis and MotorStorm Arctic Rift, but the folks at Wololo.net have found another game that runs the same program even after the update. The above video shows Wololo's Doom running on a Vita. It hasn't yet disclosed which game allows the hack.