double free

A memory bug where the same block of memory is released twice, corrupting the allocator.

When a program frees a chunk of memory, the allocator marks it reusable; freeing it a second time can corrupt bookkeeping and cause crashes or security holes. It is a classic C/C++ error. In microZeus, double free was one of the symptom counters that read zero after a fix, confirming the bug was gone.