Ever wondered whether that person tweeting incessantly about Hillary Clinton and Donald Trump could possibly be real?

Well, you have reason to be suspicious, because researchers at the University of Southern California's Information Sciences Institute have found computer bots are responsible for a fifth of all tweets about the US election.

How do they know?

The researchers analysed some of the most popular US election hashtags — including #trump2016 and #imwithher, and of course #nevertrump and #neverhillary — and came up with over 20 million tweets sent over a month by almost 2.8 million users.

They found that about 400,000 of the users were likely to be bots, and that they were behind 3.8 million or so tweets.

How did they know they were bots?

It was complicated because the bots were pretending to be human. But there are tells. Bots tend to tweet more frequently; have fewer followers; and be less likely to post from phones. Bot accounts also tend to have been created more recently and have more random names.

The researchers put the tweets through a program called BotOrNot which takes these sorts of factors into account.

What do bot tweets look like?

Here's an example from a Trump supporter:

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And here's one from a Clinton supporter:

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How did the Clinton-supporting bots differ from the Trump-supporting bots?

The study found that the Trump supporters were more positive than the Clinton supporters — and that this was true whether they were humans or bots.

As well, negative tweets from Trump supporters were usually about Clinton, whereas the majority of negative tweets from Clinton supporters were about Clinton herself.

And there was another curious finding: among Clinton supporters, human tweets were slightly more positive towards their candidate than the bot tweets were.

Should we be worried about them?

The researchers identified three areas of concerns

Bots could be operated for malicious purposes

Bots could be operated for malicious purposes Bots could further polarise the debate

Bots could further polarise the debate Bots could further spread misinformation

Their conclusion? Bots are indeed a problem:

Our findings suggest that the presence of social media bots can indeed negatively affect democratic political discussion rather than improving it, which in turn can potentially alter public opinion and endanger the integrity of the presidential election.

They say more investigation is needed to confirm who is behind the bots. It's not just political parties and foreign intelligence agencies that have the means; even individuals with enough resources could be behind them.

The study says researchers must now develop "more sophisticated detection techniques capable of unmasking the puppet masters".