The Fila Brasileiro is a breed that requires extensive socialization. It was bred to be a guard dog and herder and thus has a natural tendency to be suspicious of strangers and very defensive. This can lead it to be aggressive with any pets or people that are not part of its family. This natural aggressiveness cannot be socialized out of it completely. It can be dampened and with a very firm owner, it can take its cue on when to refrain from acting on instinct to defend and attack.
To socialize it within the home is fairly easy. It is naturally protective of small children, pets, and other people who belong in the household. It is only when strangers appear that it can be an entirely different matter to control the aggressive tendencies. The best way to start to get it socialized is through a family setting when it is a puppy. They are incredibly faithful to their own "flock" and can even take a bit of childish pranks without provocation. This patience and faithfulness to the immediate family doesn't extend to strangers, however, even if they happen to be guests in your home.
Having people coming into and out of the house, when it has not become full grown, may help it to begin to pick up the normal behaviors of strangers that are not threatening. If it doesn't have this exposure, a stranger can simply reach over to pet the dog and get bitten. In fact, judges at dog shows are warned not to pet a Fila Brasileiro because they are so aggressive with strangers.
Unfortunately, the aggressive temperament can also lead to defensive biting when it is exposed and overwhelmed by too many strangers. They might develop a fear of having strangers in the home and then react aggressively. Having people in the home will help to socialize this dog, but too many people can cause it to continue to be aggressive or feel threatened.
Most owners of a Fila Brasileiro will get obedience training for their dog. This helps it to overcome some of the natural instincts to attack without understanding that people are not provoking it. Its natural suspiciousness may not be reigned in and it may bark and snarl, but with a very firm owner and obedience training, it can be helped to control its natural aggression.
Beyond obedience training, there is aggression control training. This would be very helpful to a breed like the Fila Brasileiro. Check out different trainers to see if they have a special program to help you socialize your dog so that it is only aggressive when you decide there is a threat, and not when it thinks there is one. With a naturally suspicious nature, it can easily make a mistake and misunderstand an innocent stranger's actions for intent to harm.