What sort of doping was Operación Puerto, which hit Tour de France in 2006, about?

Explanation

Tour de France 2006 was hit by a major doping scandal, known as Operación Puerto, before the start of Tour. A Spanish doctor, Eufemiano Fuentes, was found to be systematically organising blood doping. Nine riders were excluded from the race, including the stars Jan Ullrich and Ivan Basso, who, until then, had been amongst the favourites to win that year's tour.