Decayfmt – a file format that corrupts itself a little every time you open it

Decayfmt is a novel file format that intentionally corrupts itself slightly every time it's opened, with the amount of degradation controlled by a parameter in the filename. The corruption is permanent and irreversible from the file alone, affecting both images (.idcy) and text (.tdcy) files, with higher parameter values causing faster decay. This is presented as a creative social experiment rather than a security tool, as backups or hex editors can defeat the corruption.