I have a Malshi .. 18 months old desexed male, he barks and tries to attack people all the time, how can I stop this?  Thank you?

By training and association

What is a Malshi????

You don`t give enough information to be able  to give you any positive advice, like..

Have you owned this dog since it was a puppy?  If so, did you socialise it properly? Have you done any training with it?

What age was he castrated? 

What is the dogs daily routine and exercise? 

Does he bark when on or off the lead, or Both?

Does he do this when out in public or when you have visitors, or both?

What is the dogs basic temperament like? 

Any answers given without the above info, can only be `guessing` at what may be the cause.

There can be various reasons why dogs bark and want to attack people, and without any info , its impossible to say why YOUR dog is acting this way. 

You may be better off consulting a hands on dog behaviourist who can see the dogs body language first hand. Jmo. 

A wot?   If this dog has reached 18 months and is still behaving like this, shame on you for not getting this sorted out by now.

If he's likely to attack/bite, he needs to be wearing a muzzle now.   Pity.

By training it. If you knew how to do that, you would have done it already and wouldn't need to ask this, so I suggest finding a dog trainer.

Does not matter what breed of dog you have, obedience training is a must, socialization of the dog is also a must if you are going to be living around other people and other animals.

Just to get a dog, feed it, care for it’s basic needs, get it’s shots and have it “desexed” is not enough, it needs to be taught different things like going outside to urinate and dedicate or your house will get pretty smelly if the dog doesn’t get traiNed to toilet outside.

If you don’t know hoe to train your dog, get a book, watch videos on you tube and otherwise where the trainers will explain to you how to train your dog, if you can’t figure that out or need help you can also go to a dog trainer and hire them to assist in your dogs education.

Maybe it's because you keep calling your ill bred backyard breeder mutt a Malshi when there's no such breed?

TRAIN your dog. Put a vibrating collar on this mutt so it CAN'T bark at people. Keep it on a short leash and MUZZLE IT when you go out if it's attacking people.

Why the Hell have you let a year and a half go by ALLOWING this behavior?