What is a type of malware that is so difficult to detect and remove that most experts agree that it is better to backup your critical data and reinstall the os?

A rootkit. It allows access to the private areas of your computer.

Board game basics: the main types of board games. as a general rule, board games can be divided into three categories: war games, game design is the art of applying design and aesthetics to create a game for game design creates goals, rules and challenges to define a board game, list of types of games