Illegal move or bug?

I have understood that castling is not allowed in chess if any square between King and rook is threatened. Check out move 12 of this game for white. Is it a bug or hack? My opponent disconnected himself for 2-3 minutes before that move and dc'd 2 more times in the game.

http://www.chess.com/livechess/game?id=581865201

The king can't pass through a square that is under attack and in your case he doesn't, rook can do it (here is is passing through b2 attacked by bishop). So everything is according to rules.

Neither. That move is perfectly legal. The king was not in check, the king did not castle into check, and the king did not castle through check. Lol.

The rule is that if a King moves THROUGH a square that is being attacked, which the king did not do. Perfectly legal

obiously legal

I posted a forum about that and got it explained

Castling used to fool me and scare me... 20 years ago

Ok, thank you all for clearing that up. I guess I had misunderstood the castle ruling, and disconnection just before the move made it even more suspicious for me =)