ILAN, Italy - Red Bull team boss Christian Horner has defended Ferrari, amid the controversy about secret Pirelli tyre tests conducted by the Italian team as well as Mercedes.Red Bull joined Ferrari in filing an official protest after it emerged that Mercedes used its 2013 car for Pirelli tyre testing at Barcelona following the 2013 Spanish grand prix. Then it turned out that Ferrari had ALSO done some testing... and that the International Automobile Federations was investigating Ferrari for testing tyres in Barcelona using a 2011 Formula 1 car.'WASN'T THEIR 2013 CAR'Ferrari has dismissed the test as "irrelevant", insisting the only rule breach was by Mercedes since the German team used its current car and race drivers, whereas Ferrari's test was conducted by Pedro de la Rosa and a customer's private car.Horner said: "Ferrari's position is different because even though it used an official driver (Rosa), it wasn't their 2013 car. The two situations (Mercedes and Ferrari) are not even comparable."Asked what he expected from the IAF investigation, Horner answered: "That the matter is analysed quickly and fairly."Both Mercedes and Pirelli have hit back strongly at claims its Barcelona test was conducted in "secret".HAMILTON'S MYSTERIOUS TWEETHorner said: "You have that sort of approach when you don't want someone to know something, otherwise they could have just announced it publicly, as they do for all their other activities.""Everybody in F1 is subject to the rules; teams, drivers and suppliers. The rules also apply to them (Pirelli)."It is also rumoured that Lewis Hamilton "tweeted" from America while he was actually testing in Spain and used a different helmet livery in order to avoid being identified.