SAN JOSE, Calif. — “If someone tries to shoot me, let me know,” James McGibney says, as we take a seat at a Tex-Mex restaurant. The waitress puts him facing the wall, and McGibney, a tattooed, bearded 40-year-old in a hoodie and Yankees cap, is wigging. “I never have my back to the door,” he tells me, checking over his shoulder. McGibney has reason to be paranoid. A few minutes earlier, his iPhone had buzzed with the day’s first death threat. “Chop your head off” was all it said. Last night during our dinner, he got another two: “F--- off c---. I will kill u” and “I am gonna rape your bitch wife.”

Such are the hazards of being the most controversial vigilante online. McGibney is a former Marine who battles those he deems the Internet’s worst fiends. As social media permeates our everyday lives, so do the means of harassment: posting nude pictures of an ex on Tumblr, menacing celebs on Twitter, preying on kids on Snapchat. In late August, a hacker released nude photos of actress Jennifer Lawrence and model Kate Upton on the Web forums Reddit and 4chan. But one doesn’t need to be famous to be targeted anymore. And with the ease of anonymity, it’s difficult to get the police (who often lack the skills and resources for online investigations) to intervene. That’s where McGibney and his shadowy crew of hackers and sleuths come in. They’ve infiltrated, attacked and dethroned some of the baddest bad guys (and girls) of the digital age. As McGibney puts it with his usual bravado, “I will mentally skullf--- a bully.”

McGibney first achieved notoriety with CheaterVille, a site that allowed jilted lovers to post their exes’ names and faces on a site for others to search. Today, his primary war room is BullyVille, a social network where visitors can post the names, faces and bios of their harassers for free. With thousands of victims, including high-profile celebrities, sharing their stories on the site, BullyVille went mainstream, landing McGibney high-paying advertisers, international media gigs and an upcoming CheaterVille TV show.

But the success is coming at a dangerous price. The targets of his militant campaigns say McGibney is the real bully, a vengeful egomaniac leaving innocents in his crossfire. “He hacked me and sent terrible people after me,” says one of his self-described victims — and an unlikely one at that. She’s a mother of four who tells me McGibney and his cronies claimed she was harassing the reality show star Kate Gosselin online. Others call him “McFibney” and a “fraud,” and accuse him of being no better than his supposed foes by running “a blackmail/bullying company” of his own.

In recent months, the army of vengeful trolls tweeting, blogging and plotting against McGibney has grown so vicious that fighting them off is a full-time job. But McGibney isn’t backing down. “Go after my advertisers, go after my family, go after my friends, I'm not going away,” he says. “I’m going to fight you until I'm dead.” Then he checks over his shoulder, and dips into his nachos again.