Hackers use their technical skills to access computer systems or networks. Although they share a common aim -- to find bugs, vulnerabilities and weaknesses -- they do not necessarily use their skills for the same reasons. While some hackers target systems for malicious or criminal purposes, others may not aim to do any harm or may even hack systems for positive reasons.
Hacking for Fun
Sometimes, hackers try to crack a system as a challenge -- they do it just to prove that they can. Typically, they're more interested in using their skills to find ways to breach systems than in doing anything malicious when they're in. In a PBS Frontline interview, a teen hacker who hacked into NASA said that getting into systems was a "power trip" but that he wasn't interested in the information he could then access. However, in some cases, hackers do cause malicious damage by loading viruses or malware onto systems.
Hacking for Criminal Gain
Some hackers use their skills for criminal activities. On a personal level, a hacker might break into someone's computer and take control of it -- this could give him access to passwords and financial information that he could then use to defraud the individual. On a larger scale, groups of hackers might target companies as part of a wider criminal operation. For example, in 2014, a group of Russian hackers accessed systems in various companies around the world and stole over 1 billion usernames and passwords from over 400,000 websites.
Hacking to Make a Statement
Hactivists are hackers who breach systems to make political or ideological points or to access information that they can use for these purposes. They typically target governments and businesses and often use cyberattacks such as "denial-of-service" campaigns to disable websites. For example, in 2010, the hactivist collective Anonymous used "Operation Payback" to try to take down the websites of financial services companies that had stopped processing donations to the WikiLeaks campaign, including PayPal, Mastercard and Visa.
Hacking to Improve Security
Some hackers use their skills to improve systems and security, informing companies of bugs and vulnerabilities so they can fix them. In turn, some companies tap into hackers' skills to test out systems as a defensive measure. For example, Google runs competitions and invites people to find ways to breach systems. In 2014, it ran a "Pwnium" contest that gave cash prizes to anyone who could compromise various security levels of the Chrome OS. Companies also sometimes employ former hackers to help develop and test systems and make them more secure.