It has been used almost interchangably with code rot in this sense for a long time: http://www.catb.org/jargon/html/B/bit-rot.html

> The Jargon File, a compendium of hacker's lore, defines "bit rot" as a jocular explanation for the degradation of a software program over time even if "nothing has changed"; the idea being this is almost as if the bits that make up the program were subject to radioactive decay.

https://en.m.wikipedia.org/wiki/Software_rot