While Sabu and Topiary are firmly on the inside, the likes of The Jester and LulzSec Exposed are most certainly not

Inside

Sabu Apparent founder and leader of LulzSec, he is a long-time hacktivist associated with senior Anonymous members. Decides who can join the group and who should be targeted. Attempts by rivals to uncover details about his real-life identity suggest he is a 30-year-old IT consultant skilled in the Python programming language who has lived in New York. The timing of some his tweets – tweeting "goodnight all" at 0700 BST, or 0200 New York time – implies he is on the US's eastern seaboard.

Topiary Believed to be second-in-command, and the public face of LulzSec. An eloquent writer with a sharp turn of phrase, Topiary manages the main LulzSec Twitter account and has a hand in most of the group's rare public pronouncements. Well-known among hackers due to long links with senior Anonymous members. Chat logs taken over five days from May and June show Topiary to be oddly self-conscious – he said of a Wikipedia page about himself: "can we delete it somehow?" – and not beyond his own reproach: "Sabu and I got a bit carried away and gave LulzSec away a bit." Little is known about his identity, though he has been informally addressed as Daniel in leaked transcripts.

Kayla Thought to be the only senior female member of the hacking community, with lengthy involvement in the top command of Anonymous and, latterly, LulzSec. Apparently owns a powerful botnet used to take down targets. May have been instrumental in the attack in February on a US security firm, HBGary. In logs, referred to as LulzSec's "assassin/spy".

Storm Another senior hacker apparently controlling a large botnet of infected computers. Known for targeting rival hacker forums, and acting on Sabu's instruction. Appears to be a veteran in the world of taking down websites, privately disclosing this month in logs seen by the Guardian that his denial of service tool is "over 10 years old".

Joepie92/Joepie91

Fringe member who spends much of the time "idling" in the group's chatrooms rather than actively co-ordinating or supporting attacks. Helps identify rival hackers. Little is known about his real-life identity.

Neuron One of the most technically able members of LulzSec, Neuron builds tools for the group and is occasionally involved in distributed denial of service (DDoS) attacks. Little is known about Neuron's real-life identity, although his use of "aye" for "yes" suggests he is in or from the UK.

Tflow Credited with creating LulzSec's famous Friday song, a comical skit denouncing other hackers and warning its rivals. Tflow also appears to be involved in maintenance for the main LulzSec website, protecting it from incoming attacks. Claims to have been around since the start of LulzSec towards the end of May.

Outside

The Jester Emphatically not a member of LulzSec. A lone-wolf hacker, self-described as a "hacktivist for good". Believed to be ex-military, The Jester appears to have considerable firepower, which he principally employs against jihadist websites. A thorn in the side of the sprawling collectives Anonymous and, latterly, LulzSec for some time: publicly mocking their "childish" pursuits and threatening to expose key members by releasing their "Dox": documents and information that would identify them in real life. Most believe the Jester to be based in the US, a product of his military background. He also attacks what he calls "terrorists, sympathizers, fixers, facilitators, and other general bad guys". Brought down the WikiLeaks website in November, hours before it released the US diplomatic cables, with an enormous DDOS attack.

LulzSec Exposed Group of unknown size of self-described "web ninjas" who say they are unaffiliated to The Jester, but share his desire to out members of LulzSec. Claim to be angry on behalf of victims; English may not be their first language (or perhaps not that of the person(s) writing their blog. "We are not doing this for [the] sake of publicity or media attention," they say on their blog. "We just thought we could help and we did it."