Anyone with a clue.

Unsigned values in C and C++ are a leading cause of bugs, including security bugs.

Unsigned size_t was a major flaw. STL size() returning an unsigned value just made it worse.

Anyone who codes in C or C++ knows this.

This result required the use of *many* computers to solve *many* positions (approximately four million billion positions), and each found solution was 20 moves or less.

Yes, in some terms it was brute force, but consider how big a number four million billion is, and how long it takes to solve just a single position in 20 moves or less.