Subramanian said hacktivists don't just want to disrupt services; they also want to undermine public trust. "That is what is going to move the hacktivists to continue to do this."
Hacktivists are an amorphous group. While some may be individuals unhappy with a perceived social injustice, many are linked to loosely associated networks such as Anonymous, a major hacktivist group responsible for attacking government, corporate and religious websites.
Anonymous describes itself on its website as a "relatively small vigilante cyber group" that has "expanded and transformed into a continuation of the Civil-Rights movement."
Hacktivists use various tools: Sometimes, they hack into private email or confidential records and make them public. Sometimes, they compile personal information about targets such as police officers from the internet or government record breaches and post it online, which is called "doxing" (a derivative of "docs," slang for documents). The information can include a person's home address, phone number and even the names of his children. Hacktivists see it as transparency; security experts see it as harassment.
Often, hacktivists launch "denial-of-service" attacks, in which they try to knock a website offline by flooding it with traffic. To do that, they take control of a large group of computers -- sometimes tens of thousands or more -- using malware that unsuspecting people have launched on their home or office computers by clicking on an email with an attachment or a link to a website. The hacktivists then control the so-called "zombie" computers and direct them to bombard a specific website with traffic at the same time, causing it to freeze.
"A given website can only handle so many visitors," Calkin said. "When you exceed that number, the server will crash. When you keep that attack up, there's no way to recover it while it's happening."
If a government computer system doesn't have the protections to block such attacks, a website can be knocked offline anywhere from several minutes to 24 hours or longer.
Experts generally don't consider cyber espionage by foreign governments or intelligence agencies to be hacktivism. But some do include groups such as WikiLeaks, an international organization that publishes secret or classified information, some of which has been hacked by others with political or social agendas.
"Hacktivism isn't just about crashing systems or bringing down websites," Lohrmann said. "It's hacking to achieve the ends of social or political causes. It could be stealing information or publishing information to embarrass or discredit people."
Some hacktivist attacks have been successful; others haven't.