self-modifying code 

When bad programming (or a bad compiler/loader) causes a computer to 'write' data over a portion of memory that it later thinks is programming instructions in machine code, it will end up doing unpredictable things, depending on that data. By extension, any action which is likely to have unpredictable, unforseen or chaotic results.

Usually heard among techies who program in assembly language or machine code.

"I wouldn't tell your wife about your one-night stand in Tulsa if I were you; that would be self-modifying code."

self-modifying code by Meles Borealis January 11, 2009