Hacking is a loose term that’s often used incorrectly. Traditionally, it refers to illegally gaining access to a computer network. In the context of an iPhone, hacking could refer to any of the following:
Gaining access to someone’s private information stored on an iPhone.
Monitoring or using an iPhone remotely without the owner’s knowledge or consent.
Changing the way an iPhone operates by using additional soft- or hardware.
Technically, someone guessing your passcode could constitute hacking. The installation of monitoring software on your iPhone so someone can spy on your activities might also be something you’d expect a “hacker” to do.
There’s also jailbreaking, or the act of installing custom firmware on a device. This is one of the more modern definitions of hacking, but it’s also widely used. Lots of people have “hacked” their own iPhones by installing a modified version of iOS to remove Apple’s restrictions.
Malware is another problem that’s hit the iPhone before. Not only have apps on the App Store been classified as malware, but zero-day exploits have also been found in Apple’s web browser, Safari. This allowed hackers to install spyware that circumvented Apple’s security measures and steal personal information.