illegal move allowed?

game 402514 move 18 - rook (not king) moves across attacked square to castle. one player thinks this is illegal and the other thinks it may be legal for rook, but not king. We are happy to let the game continue as is, but believe this is may be a program bug.Game 402514

No this is a legal move, during castling as long as the king does not pass through a square that is being attacked (in effect checking king) then the move is legal. Although the rook passed through attacked square this is legal.

-Robbo

I never knew that was legal! that is really good to know... 🙂

Yep just to clarify this here are the basic rules of castling as found in FAQ section of this site.

All the sqaures between your king and rook are unoccupied.
The king has not moved yet
The rook involved in the castle has not moved yet
The king is not in check
The king will not move into check
The king will not move through a square being attacked

-Robbo