He has defaced and shut down hundreds of terrorist websites, inserted false stories into Libyan newspapers, and unmasked fellow hackers who have crossed him.

He goes by the name "The Jester," and he has worked alone as an anonymous hacker vigilante since 2010.

Though the international "hacktivist" group Anonymous declared cyberwar against ISIS on Sunday, The Jester is not among them. In fact, he is among the group's sharpest critics.

"All they'll do is dump a random list of names from a previous hack and claim it's ISIS members, and they'll report 'ISIS' accounts to Twitter. Pretty standard BS from them," The Jester, who uses the @the3j35t3r Twitter handle and keeps his identity closely guarded, told Tech Insider in an interview over Twitter.

In a video released to YouTube after the terrorist attacks on Friday night in Paris, Anonymous vowed "massive cyberattacks" while launching its "biggest operation ever" against ISIS. The group then released a listing of nearly 10,000 Twitter accounts it said were linked to ISIS.

This isn't the first time ISIS has drawn the scorn of the hacker collective. In August 2014 the group also "declared war," later revealing what it said were about 10,000 ISIS-linked social-media accounts, according to The Christian Science Monitor.

But even Anonymous may err amid a confusing battlefield in Iraq and Syria. Along with its listing of websites that are clearly in support of the Islamic State, there were others that were questionable: One site had nothing more than placeholder content (headline: "Modern Concept And Charming Kitchen Design Ideas"), while another was an academic research site intended to track Russian-speaking foreigners who travel to Syria.

On Tuesday, Anonymous posted a listing of people it said were suspected ISIS extremists with a warning: "We are coming for you." And on Twitter, an Anonymous-affiliated hacker who goes by @CtrlSec — his or her bio lists a website for people to report terrorists online — began posting what the hacker said were ISIS-related Twitter accounts. Still, the group has been accused of misfiring in some past releases, and a simple listing of first and last names can be hard to verify as ISIS supporters.

"In the past it's been limited to getting accounts suspended, getting content taken down, identifying IP addresses," Dan Winter, a security specialist, told the BBC of Anonymous. "But it's disruption rather than meaningful challenge. It won't solve the problem. It'll be interesting to see if it goes further than they have before."

Interestingly, there may be some internal strife within Anonymous over its latest operation. Tech Insider reached out to multiple social-media accounts affiliated with Anonymous with no response. But "X" — the preferred nickname of an Anonymous hacker who claims to spend nearly 12 hours a day conducting business on the group's behalf — did respond over email.

"While I do not oppose Op ISIS, I do not agree with it nor will I actively support it," X said. "And I am not alone within Anonymous in this position. The reason is simple. The primary beneficiaries of Anonymous Op ISIS is NATO and the government of the USA. These very same organizations have long listed Anonymous as a 'foreign terrorist group' right along with ISIS, and for this reason Anonymous has been for several years at war with NATO and the USA. It seems rather foolish to me to be aiding our mortal enemies, who lock up and even torture Anons — in a fight against an evil that they themselves actually created."

But The Jester doesn't expect much from a group he calls "blowhards": "It's the usual case of Anonymous jumping on a current big news story," he said. "It'll amount to a hill of beans like always."

With the group offering members complete anonymity and no real leadership, The Jester argues, it could even host jihadists and other bad actors within its ranks.

But X counters this view, telling Tech Insider that while there is no central command structure, Anonymous does operate cells that are coordinated with internal leadership. And he says these cells take precautions and distrust potential infiltrators unknown to them in chat rooms and social media.

Flickr/Brian Klug A self-proclaimed patriot hacker, The Jester actually got his start by going after Anonymous members and Wikileaks, which he believes endangered the lives of US troops with its massive release of classified data obtained from Chelsea Manning. But The Jester's real passion, it seems, is going after jihadists online.

"I am here to say — no guys — you ain't gonna use the web to blow my buds up," The Jester told a hacker conference in 2011, making a vague reference to having a military background. He told TI, "I'm a former military man, but when pushed I tend not to go there." (In one interview, he claimed to have served as a soldier with or attached to Army Special Forces, while a New York Times report said he used to be a military contractor).

"Approximately five years ago I realized that there was a growing threat from jihadis online using the internet to recruit, radicalize, and even train homegrowners," The Jester told NBC Chicago. "I decided to research their favorite haunts, collect intelligence on the users and admins and in many cases remove them by force. I tended to hit some sites a lot and leave others. This had the effect of herding/funneling them into a smaller space. And smaller spaces are easier to watch and monitor."

Since then, The Jester has built tools that initiate distributed denial-of-service, or DDoS, attacks that are able to take websites offline. He has also coded tools that have fooled hackers in Anonymous, complete with backdoors that have revealed their identities — a move he says has earned him plenty of attacks in response. But nearly every time, he documents his apparent successes with his calling card: "Tango Down," a callback to military phrasing meaning that a target has been neutralized. According to a CNN Money report, the hacker says he stopped counting at 179.

Unlike Anonymous and its mish-mash of websites and Twitter, Facebook, and YouTube accounts, The Jester is easily found online in a handful of places, and he sometimes gives live cybersecurity talks (though he presents only through text chat to conceal his identity). He documents his hacks and comments on information security at his blog, and his nearly 70,000 Twitter followers are privy to his threats toward jihadists, and the follow-up successes if they occur.

After he researches target websites and identifies them, he'll attack — and often tweet as its happening. "www.alemarah.info is now under sporadic cyber-attack. This 'Voice of Jihad' served only to act as tool for terrorist [sic]. OWNED. By me, Jester," he tweeted in January 2010.

Sometimes, he'll warn hosting companies they have a site on their servers with jihadist materials. "U should take action, or if you prefer, I can," he tweeted in June 2014. He closed with the hashtag #30mins, and as promised, he announced "Tango Down" approximately 30 minutes later.

It's far too early to tell whether Anonymous' war on ISIS will be what The Jester refers to as a "hill of beans."

Still, on Tuesday he praised the group for its stand against Scientology in 2008, though even that was a backhanded compliment within his overall critique: "I'm not saying [Anonymous] ... doesn't have good intentions," he wrote on his blog. "I am saying they don’t have the skills, situational awareness, or moral fiber to back that up."