Australian police say they have arrested a "self-proclaimed leader" of the hacking group LulzSec.
The 24-year-old from New South Wales is accused of attacking and defacing a government website earlier this month, a police statement said.
Lulzsec has claimed responsibility for several high profile cyber-attacks, including against Sony Pictures and the CIA.
It emerged as a splinter-group of hacking collective Anonymous in 2011.
In the statement, the Australian Federal Police said that the arrested man was an IT professional who used his position in an IT company to access sensitive information from clients, including government agencies.
He has been charged with two counts of unauthorised modification of data to cause impairment, and one count of unauthorised access to restricted data. He faces a maximum of 12 years in jail.
"Those thinking of engaging in such activities should be warned that hacking, creating or propagating malicious viruses or participating in Distributed Denial of Service (DDoS) attacks are not harmless fun," Cyber Crimes Commander Glen McEwen said.
LulzSec gained international attention when they hacked the Sony website in 2011, taking down the company's PlayStation network for weeks and accessing millions of users' accounts.
It was estimated to have cost the company over $100 million (£65m) and was part of a 50-day rampage which targeted organisations ranging from the FBI to Britain's Serious Organised Crime Agency.
The name stood for Lulz Security - in which "Lulz" is derived from the popular internet term "lol", meaning "laugh out loud".
The group's members employed techniques to flood websites with high traffic - known as DDoS attacks - in order to render them unusable.
