They go by names like Anyonymous, Lulz Security, Zeus, Night Dragon, Green Army Corp, Inj3ector Team; their goals, methods, effectiveness vary
Hacker groups that attack or steal — some estimates say there are as many as 6,000 of such groups online with about 50,000 “bad actors” around the world drifting in and out of them — are a threat, but the goals, methods, effectiveness of these groups varies widely.
Malicious activity alert: Anonymous hack-school grads come online in 30 days
When they’re angry, they hack into business and government systems to steal confidential data in order to expose information about their targets, or they simply disrupt them with denial-of-service attacks. These are the hackers with a cause, the “hacktivists” like the shadowy but well-publicized Anonymous or the short-lived Lulz Security group (which claimed to have just six members and just joined forces with Anonymous).