Bit rot

Есть такой эффект bit rot - самопроизвольное изменение данных, даже если с ними не работали.
"Bit rot, also known as bit decay, data rot, or data decay, is a colloquial computing term for the gradual decay of storage media or a (sometimes jocular) explanation for the degradation of a software program over time, even if ‘nothing has changed"
http://en.wikipedia.org/wiki/Bit_rot#Decay_of_storage_media