Trolling is a very modern phenomenon that has no signs of abating any time soon.

Many news sites have resorted to removing their comments sections below articles because the remarks became so bad, and increasingly anti-trolling systems are being brought into place.

Norwegian public broadcaster NRK, for example, is trialling a system that makes people answer a question about the article before they’re allowed to comment, thus ensuring any potential trolls are at least informed.

And a project by Google created an ‘application interface’ that is meant to spot abusive comments and reject them before the troll’s words will appear.

Trolling has become something of an epidemic, but why so many people do it is a mystery - surely there can’t be that many hateful people in the world? Why do trolls spread so much vitriol online that they wouldn’t dream about doing in person?

Well, new research has discovered why and how normal people turn into trolls on the internet.

A study conducted by Stanford and Cornell Universities in the US has determined that the anonymous people who post cruel, unpleasant and unnecessary comments could be any of us - we all have the potential to become a troll.

“We wanted to understand why trolling is so prevalent today,” said lead author and Stanford computer science researcher Justin Cheng.

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He sought to determine whether the people who troll others online have some innate trait that makes them do so, or whether their actions are influenced by “situational factors”.

The study concluded that the reason someone trolls is based on two factors: the person’s mood and the tone of other comments.

The researchers asked 667 people to do a test - some were given easy ones, others more difficult, on the presumption that those who’d done the hard test would be in worse moods afterwards.

After completing their tests, the participants were then asked to read an article and post in the comments section underneath.

The results were remarkable.

All participants were given the same article with three comments already there, but the comments weren’t all the same - some people saw articles with three neutral, inoffensive comments underneath, but for others the comments were by trolls.

Only 35 per cent of people who’d completed the easy test and viewed inoffensive comments went on to write trolling comments themselves.

Of those who’d either undertaken the tricky test or read the troll’s comments, about half went on to post nasty comments themselves.

And this number rose to 68 per cent for people who’d both done the difficult test and read the trolls’ comments.

Which comments qualified as trolling was identified by two independent experts using guidelines from several discussion forums - personal attacks and cursing, for example, were considered signs of trolling.

To further back up their findings, the researchers analysed the data of over one million users, 200,000 discussions and over 26 million posts in CNN’s comments section, including comments by banned users or ones that had been deleted by moderators.

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The researchers looked at the times the worst comments were posted “because previous research has shown that time of day and day of week correspond with mood.”

They found that trolling comments were more likely to be posted late at night and early in the week, which is when people are most likely to be in a bad mood.

This has been proven by previous research that has shown people are most likely to post negative comments between 10pm and 3am on Sunday and Monday nights, and that Twitter bullying is at its most severe on Sundays between 5pm and 8pm.

Delving further into the effect of mood, the researchers discovered that people were more likely to produce a flagged post if one of their own comments had recently been flagged or if they’d contributed to another discussion that included flagged posts.

Associate professor of computer science at Stanford and senior author of the study Jure Leskovec explained it thus: “It’s a spiral of negativity. Just one person waking up cranky can create a spark and, because of discussion context and voting, these sparks can spiral out into cascades of bad behaviour.

“Bad conversations lead to bad conversations. People who get down-voted come back more, comment more and comment even worse.”