Editor's note: This report contains explicit language that some readers may find offensive.
London (CNN) -- Curtis Woodhouse earns a living punching people in the face, so it's fair to say he's one of the last men you'd hurl insults at if you saw him on the street.
But people tend to be a bit braver once they don the anonymity cloak the internet provides, and the 32 year-old English boxing champ faced a flurry of ugly abuse from trolls online after he lost his most recent bout in March.
One particular troll, @Jimmyob88, had been harassing the boxer in tweets and in direct messages for six months, according to Woodhouse. "He'd threatened my children saying 'be careful where you send them to school,' he threatened my wife. He'd written me saying he hoped I'd die in my next fight so I could go and see my dead dad ... it just went on and on."
But after the bully branded the boxer a "disgrace" and a "complete joke" and urged him to retire following his fight last month, Woodhouse finally snapped and, rather than trade blows online, he used Twitter to turn the tables on his troll.
Woodhouse put a "Twitter bounty" out on @Jimmyob88's head, offering anyone £1,000 for information about the user's real identity. Within minutes he had his troll's real name -- James O'Brien -- some photos of O'Brien and his home address. Woodhouse decided to make a house call.
"I wasn't going to beat him up or anything," Woodhouse told CNN. "I was going to knock on his door and say 'listen, this stops today -- I'm not going to put up with this abuse, you have no right to abuse me and my family.'"
"I put the address into my sat-nav and it said I was 47 miles away from my house to his house. So that's when I put the wheels in motion, sent him a message saying 'I know who you are, I know where you live, and I'm on my way.'"
Woodhouse hopped into his car and headed from Hull, in northeast England, to Sheffield, updating his followers on Twitter as he drove. O'Brien continued heckling him at first, perhaps not believing the boxer was actually en route, but that all stopped when Woodhouse wheeled onto his road and posted a photo of his street sign online.
Woodhouse tweeted: "right Jimbob im here !!!!! someone tell me what number he lives at, or do I have to knock on every door".
As it turns out, O'Brien wasn't at home at the time, but he quickly apologized to Woodhouse: "@jimmyob88: @woodhousecurtis i am sorry its getting abit out of hand i am in the wrong i accept that".
Woodhouse headed home, satisfied. "The whole world saw him for what he really was, which was a coward and a bully, and the way I saw it, my job there was done."
Twitter antagonists like O'Brien are a relatively new breed of online "troll" -- people who post abusive content online with the aim of offending or provoking someone else into a reaction -- but cyberspace bullies have been around as long as the internet itself.
In the late 1980s, Usenet users began using the word "troll" to describe someone who deliberately disrupted online discussions in order to stir up controversy, according to Whitney Phillips, a New York University lecturer who is currently writing a book on trolling behavior.
"'Troll' was a name you called someone else," she told CNN. "More frequently you reacted to being 'trolled' than you identified yourself as a troll."
Phillips says it wasn't until the mid-2000s when the predominantly anonymous users of 4chan -- the website CNN once described as "one of the seedier, darker corners of the Internet" -- began to describe themselves as trolls.
As the freewheeling site's controversial "/b/" board rose to prominence, garnering media attention for everything from LOLcats and Rickrolling to allegations its users were exchanging child pornography, "trolling" evolved into an unwieldy umbrella term that Phillips believes is preventing us from considering the wide range of behaviors the word now describes.
"You can't easily taxonomize trolling behavior," she said. "A lot of trolling is about mischief and harmless, silly pranks. But really extreme behavior -- attacking friends and families of kids who have died, for example -- that seems to be a behavior with a different motivation."
In April of this year Rehtaeh Parsons, a 17-year-old high school student from Nova Scotia, hanged herself after a photo of her allegedly being gang-raped by four boys was posted online. But the abuse continued long after Parsons died.
A Facebook memorial page created for Parsons after her suicide was targeted by trolls, one of whom wrote: "lol, teach your kids not to be huge p****es and they'll take care of anyone who's bullying them." Another wrote: "She wasn't bullied for being a rape victim, she was bullied for being a sl*t, which she was."
The comment section on one of CNN.com's stories about Parsons was flooded with a similar flavor of bile. Within hours of the story being published, a user called "Cookie Monster" wrote "Thank god she got justice" and told another commenter to stop "acting like a 12 year old cancer patient" -- and these were some of the less grim offerings on the page.
So what kind of person trolls strangers online? Jerry Holkins and Mike Krahulik, creators of the Penny Arcade webcomic, offer up an explanation known as John Gabriel's Greater Internet F**kwad Theory, consisting of the following equation: "Normal Person + Anonymity + Audience = Total F**kwad".
The math may a bit fuzzy, but there's something to that equation. The anonymity users have on the internet is a big factor in the "online disinhibition effect," which Rider University psychology professor John Suler says enables people to say things to each other online that they wouldn't say in person.
"Without face-to-face presence, a potential troll is more likely to perceive others as a 'target' rather than a real human being," he told CNN.
If anonymity is one factor, psychological and emotional issues are another, according to Suler, who says many trolls likely have problems with depression, low self-esteem, and anger.
"They want to inject their own emotional turmoil into other people by luring them into negativity. It's a way for them to feel some kind of control or power over their own disruptive emotions, at other people's expense."
While Whitney Phillips agrees that anonymity plays a role in someone's propensity to spew bile down Facebook walls, Twitter pages and news website comment boards, she says the bile was there first, just waiting to be hurled out at unsuspecting passers-by in cyberspace.
"The problem with blaming anonymity is that it assumes people are only horrible anonymously. Search a racial slur plus Obama on the internet and you'll see more people than is reasonable who are perfectly happy being disgusting bigots under their own name."
Is it possible to separate your online behavior from who you really are? Many trolls reject any relation between their profiles on the Web and their real life personas, according to Phillips, and say they are merely performing in order torment their targets "for the lulz," or to teach people a lesson.
"Some trolls think that spending your time posting condolence messages on Facebook to someone you've never met is weird, and grounds for being trolled. They think they're teaching people a lesson, teaching people how to behave online."
Ultimately, Phillips says, it's impossible to definitively say what makes trolls tick when you don't have any demographic details about them. "We can't very easily or in any kind of verifiable fashion sit a troll down and ask him what is in his heart, and if you could he would lie. They would tell you some bulls**t about what's in their heart."
No one Phillips interviewed was willing to speak for publication -- her trolls are mostly done with speaking to the media, she says -- but CNN has its own stable of comment board trolls, a handful of whom answered questions via email for this article. An email address is all users need in order to post comments on CNN.com, so it is impossible to confirm their identities or the veracity of their remarks.
"GG" declined to give her real name but described herself as an American thirtysomething with a finance degree who trolls CNN's comment pages in tandem with at least a dozen other users -- "engineers, professionals, mothers, fathers and at least one grandpa," she said.
As far as comment trolls go, GG's posts -- which she says number in the thousands -- are relatively tame: Jokes about oral sex on a story about a sinkhole which swallowed up a man in Florida in March; dreams of Anne Hathaway being "impaled on wooden stakes and set on fire" on a story about the actress.
"We mostly deal in humor," GG told CNN. "It's a creative outlet to exercise wit, blow off steam, deal with boredom and (it) provides entertainment."
Another troll, "MK", explained: "The belief that anyone truly cares about other people's opinions on an online forum is ludicrous. It's arrogant and needs to be checked." "RR" wrote: "I do it because it makes me giggle. Fellow trolls make me laugh. Some of the terrible things that happen every day should be muted with humor."
GG says her friends don't post on stories involving children dying. "There was a group moratorium on any posts regarding Sandy Hook ... There are certain topics which are just not funny."
Funny or not, there is evidence to suggest that comment trolling is preventing us from thinking rationally about the stories we read online.
In a recent study, University of Wisconsin-Madison researchers asked more than 1,000 people to read a blog post about nanosilver technology. Half of the participants were exposed to civilized reader comments on the post, and the other half were subjected to profanity-laden screeds and putdowns.
"The results were both surprising and disturbing," researchers Dominique Brossard and Dietram Scheufele wrote in the New York Times. "Uncivil comments not only polarized readers, but they often changed a participant's interpretation of the news story itself."
Scheufele told Mother Jones that reading a story online today is like "reading the news article in the middle of the town square, with people screaming in my ear what I should believe about it."
So what can be done to keep the trolls at bay? Where is the line between trolling and harassment? While most trolling behavior isn't of a criminal nature, many countries' harassment laws extend to cyberspace, and a handful of bullies have been jailed recently for crossing that line in the eyes of judges.
In October a judge handed down a 12-week prison sentence to David Woods for posting sexually explicit remarks on his Facebook page about April Jones, a five-year old girl who went missing in Wales.
British student Liam Stacey was also jailed last year for 56 days for posting racially abusive tweets about Bolton footballer Fabrice Muamba after the player went into cardiac arrest during a match. As Muamba lay struggling for life on the pitch, Stacey tweeted "LOL f**k Muamba he's dead !!! #Haha" and followed it up with a handful of racist posts aimed at other users.
Did Stacey's punishment fit the crime or was it over the top? And where should we draw the line between free speech, censorship and privacy?
Britain's politicians are considering new laws that would require websites to reveal the identities of trolls who have posted defamatory content about other people online.
In Italy prosecutors aren't only going after cyber-bullies, they're also threatening action against the social media sites themselves.
The January suicide of 14-year-old Carolina Picchio, who threw herself out of her bedroom window in Novara after a group of boys posted a video of her in the bathroom of a party, has prompted Italian authorities to consider bringing charges against Facebook staff for allowing the abusive content to be posted on the website, according to media reports.
In May, bowing to pressure from activists and advertisers, Facebook announced plans to ramp up efforts to delete hate speech, particularly depictions of violence against women, on its site.
"In recent days, it has become clear that our systems to identify and remove hate speech have failed to work as effectively as we would like, particularly around issues of gender-based hate," Marne Levine, a Facebook vice president in charge of public policy, wrote in a post on the site.
Stamping out serious abuse on sites like Facebook may be a step in the right direction -- but any law aimed at curbing online trolling runs the risk of casting a net so wide that it snares non-trolling behaviors as well, say critics.
"There are a number of online behaviors that are annoying, but do you really want to illegalize annoying behavior?" asks lecturer Whitney Phillips. "The push to illegalize these poorly defined behaviors isn't actually addressing the root issues of trolling."
David Aaronovitch of The Times newspaper in London says most online abuse would go away if we simply pulled away the cloak of anonymity that emboldens trolls.
"If you're not going to moderate comments on your site, insist on registration and lack of anonymity," he told CNN. "If you had to register under your own name and comment under your own name, who's going to be a s**tbag under those circumstances?"
CNN troll GG wouldn't, for one. "Of course not," she told me, "Who would risk a 6 figure salary on the chance that your employer disagrees with your opinion or off-hours activities? No one."
At the end of the day, the best way to deal with trolls is to simply ignore them, says Aaronovitch.
"You simply have to decide how much attention you want to give them, and grow up really," he said. "It's about saying, 'How threatened am I really by this?' and reserving your ire for the cases when there really is some serious harassment going on."
Whatever you do, hopping in your car and driving to your troll's house may not solve all of your problems, as boxer Curtis Woodhouse found out.
"Ever since I did that the abuse has been 10 times worse," he said with a laugh. "Now I've got people saying, 'If I call you a crap boxer, will you come round my house for a cup of tea?'"
CNN's Doug Gross contributed to this report.