Scribble

n. To modify a data structure in a random and unintentionally destructive way.

"Bletch! Somebody's disk-compactor program went berserk and scribbled on the i-node table."

"It was working fine until one of the allocation routines scribbled on low core."

Synonymous with trash; compare mung, which conveys a bit more intention, and mangle, which is more violent and final.