The answer may depend on which side of the PC you're sitting. It can mean sitting behind a computer all night to see if you can make a clever program to perform some useful or useless function. Not any more. During the past few years, hacking has irreversibly become equated with criminality and malicious damage to IS systems. Hackers have been mythologized, demonized, and blamed for a spectacular range of cybercrimes and invasions of privacy.
Some hackers argue that there's a distinction between harmful and harmless hacking.
Hackers say that unauthorized entry to a network doesn't have to involve harming that network or stealing intellectual property. The dividing line comes when hackers disrupt other people's uses of computing systems, in which cases they may be doing harm to others.