Sony recently yanked two games from the PlayStation Store because they found a vulnerability to hacker Wololo's Vita exploit - commonly known as the "Vita Half-Byte Loader" (VHBL). VHBL allows unsigned code - homebrew or code that has not been approved by the platform holder - to run in the PSP emulator.
The latest game found to be vulnerable to the exploit is Super Collapse 3 for PSP. After 24 hours of being released and being named on the VHBL site as a game that worked with the emulator, the game was yanked in North America and Europe by Sony.
Wololo claims that the VHBL cannot be used to run pirated games because the exploit only enables unsigned code to run in user mode - not at the root permission level that would be required to launch games.