A denial of service (DoS) attack, which shuts down a system to restrict consumer access, is an example of hacktivism. Other examples include giving citizens access to government-censored online pages or providing endangered groups with privacy-protected communication channels (such as Syrians during the Arab Spring).
Real-life example of Hacktivism:
Attacks that systematically send so many requests to a server that it cannot handle the load and is made momentarily unusable, bringing down websites or generally disrupting Internet activity. Email bombing and web sit-ins are two common examples.
Website defacements are cyber-attacks that alter the content of websites, usually to propagate a political message.
Internet Worms are programs that are designed to spread throughout a network, either to interrupt activity or to propagate a message.