As with any jailbreak or rooting of a handset, "hacking" a phone OS is usually exactly that: exploiting a weakness to get unsigned code onto a device. That means that any other hacker, be they sufficiently nefarious, could use that same exploit to mess with your phone in the bad, not-installing-emulators-off-of-Cydia sense. Early iPhone jailbreaks (back when installing your own ringtones was a wild idea) took advantage of a TIFF exploit, the recent EVO 4G root found a hole in Flash Lite, and the
