A pair of older PSP titles have have been pulled from the PlayStation Network thanks to a potential vulnerability. Sony says it's simply to fix "stability iimprovement." Meanwhile, the unofficial line from a member of the homebrew community calling him or herself W. Ololo says that their team has found an exploit in both games that will simply allow them to play emulated games.
In either event, both games are currently unavailable, and at this time, Sony hasn't announced any kind of timeline for when they'll be back. Understandably, Sony is playing this super-safe given the very tumultuous, very publicly down time that PSN had last year as hacktivists, some claiming to support George "geohot" Hotz, who was sued by Sony for gaining read/write the software of the PS3. That debacle resulted in over 77 million users' information being exposed.
So yeah, even if Hot Shots Golf and MotorStorm: Arctic Edge aren't exactly high profile system sellers, Sony's probably wise to cover themselves for the time being.
[Source: Giant Bomb]