Aggressive behaviors include things such as growling, snapping, barking, lunging and in some cases biting. These are dangerous behaviors that are not to be taken lightly and cannot be solved over night. There are many things you can do to help solve this problem, one of these however doesn't include trying to get help over the internet. Trying to diagnose and solve aggression cases over the net can be dangerous and can lead to more problems. If you are on the other end, meaning someone is asking you how to solve an aggression case you should always suggest the following:

Talk to a Vet

Dogs that show aggressive displays all of a sudden or for no apparent reason should be checked by a vet to make sure that something is not physically wrong with them. Things like severe pain or homonal imbalances often may cause a dog to display this sort of behavior. Medication and treatment of a ailment (if it exists) will usually cure these aggressive tendencies.

Get Professional Help:

Like mentioned above, never try to solve or diagnose an aggression case on your own. Its always best to refer to someone that is qualified in the field. A professional dog behaviorist can create a plan to help manage or even stop the aggression. If you need help finding one ask your vet for a referral or look in the Association of Pet Dog Trainers (APDT) website.

Determine what Triggers the Aggression

The owner should be fully aware of what thing or things trigger the dog's aggressive behavior. Once this is done you can help the situation by avoiding these triggers until you can get professional help to manage the aggression. This step is not meant as a way to diagnose but simply to avoid situations in which someone or something might get hurt.

Be Consistent, Patient, and Positive

With the help of a professional the two of you should be able to make a plan to help rehabilitate the dog. Once this is done try to never use aversive techniques to try to make a situation right. Punishments will usually tend to only make the situation worse. Always be consistent and never give up, it may take a long time for the dog to abandon those aggressive tendencies. Also be patient in the sence that you don't go farther than what your dog can take. If the plan is to take it step by step then don't move on to the next phase until you are certain that the dog is ready.

Last Resorts

Medication: Sometimes an aggressive dog may need medication to help mitigate the behavior. Never rule it out as a quick fix, it can be of great help to be able to get a dog under control and then start the program advised by the professional you've contact.

Rehoming: If you notice that your situation doesn't conform to a training schedule set by a professional (such as having a dog that is aggressive towards children but you having kids at home), it may be best to rehome the dog or give it to someone that is qualified to be able to help them. Never give a dog to someone without telling them the situation, that is dangerous and in some cases you can still be liable for damages.

Euthanasia: In some extreme cases, dogs may simply not react to any treatment. If aggression doesn't dissipate then its sometimes may be best to consider humane euthanasia as an option.

Reference: http://dogs.about.com/od/dogtraining/a/aggression.htm?nl=1

very good information to have. i haven't been around very many aggressive dogs, but every owner should at least read this

Not to make light of aggression, but many people really don't understand canine posture very well and mistake normal behavior for aggression.

Even in play, a dog can go a bit over the edge, and humans need to know calming signals.

Most displays of aggression occur when a dog who is fearful receives an extra push, and they feel they need to respond quickly to stop whatever is making them afraid.
Too many times owners misinterpret normal behavior and become tense or fearful themselves, which the dog sees very clearly, and then responds to.

That being said, it hopefully makes some sense that aggression could be easily diffused if humans better understood their dogs.