The HAARP technology is based on another invention of Nicola Tesla. The original intention of the inventions was good, it was going to provide free electricity for everybody in the world.
The basic concept was to send an electrical pulse into the atmosphere, and as the electrical pulse travelled around the world, it would collect energy from the atmosphere. After it circled the earth and returned to the station that sent the pulse (stronger than before because of the energy it collected from the atmosphere), it would be hit again with a electrical pulse. This would happen over and over as it circles the earth, and it would continue collecting energy from the atmosphere and become stronger.
When the energy was built up enough in the atmosphere, people could run electrical devices, cars and other machinery that have the right kind of antenna and other parts to gather the energy from the atmosphere. He tested this concept and was able to power light bulbs several miles away from the station without wires.
When he approached one of his regular investors with the idea, the investor wasn't interested, he said that he couldn't make money from it because it was free energy. Anybody would be able to use it if they have the proper antenna.
After Tesla looked into it more closely, he decided to hide or destroy the designs because he realized that it could be used as a weapon, and people were too wicked in the world to resist using it as a weapon.
The ways it could be used as a weapon, is if somebody has the right equipment, they could cause an energy pulse to be concentrated on a city and completely destroy it, and people could also use it to control the weather. Another thing, the frequency of the energy that is used from the atmosphere is the same frequency our brains work with, so there was a possibility that it could be used as some form of mind control or at least mind influence.