“We mostly think of hacking as the act of breaking into secured systems to determine their flaws and explore it. It simply is the modification of a piece of hardware or code to perform differently. It also includes modifying the system's hardware to make it work better and faster.”
That briefly tells us about who and what these guys are.
These are the guys that mostly points out flaws in systems and also show how to make them perform better.
Some of these guys learn how to secure information(sometimes alone) and as a result discover techniques on how those systems can be breached or perform better and draw out plans together with corrective measures and when it reaches into the wrong hands, it's misused. We have a good number of advanced technologies today which most of them have undergone improvements as a result of the flaws that have been pointed out to the companies or public. Look at technologies like windows 7.
The world is made up of bad and good. You can choose on what side you want to be.