There is a malware designed only to encrypt certain files, such as images. There is also a malware type that does that but spreads through wifi and kills itself afterwards.
Crap, my brother has an iPhone so I'm pretty sure he can't download a virus unless he jailbreaks, He hasn't and he only uses the app store and youtube, he said he rarely downloads anything and he got the "image glitch" after the power went out here shortly. sp00ky