When you conduct a poll of human beings and ask them who won each of the two presidential debates (the third is tomorrow) they mostly say Hillary Clinton. But millionaire Donald Trump overwhelmingly wins on web-based polls. Why? The fabled alt-right internet hordes crusading around the internet clicking the lot? Maybe. But his fandom is also winning the bot war, with automated robotweeting and online interaction efforts that far outstrip those of their adversaries.
Bots are social media accounts that automate interaction with other users, and political bots have been particularly active on public policy issues, political crises, and elections. We collected data on bot activity using the major hashtags related to the U.S. Presidential debate. In this brief analysis we find that (1) Twitter traffic on pro-Trump hashtags was roughly double that of the pro-Clinton hashtags, (2) about one third of the pro-Trump twitter traffic was driven by bots and highly automated accounts, compared to one fifth of the pro-Clinton twitter traffic, (3) the significant rise of Twitter traffic around debate time is mostly from real users who generate original tweets using the more neutral hashtags. In short, Twitter is much more actively pro-Trump than pro-Clinton and more of the pro-Trump twitter traffic is driven by bots, but a significant number of (human) users still use Twitter for relatively neutral political expression in critical moments.
Politicalbots.org is the source of the non-peer-reviewed report, which is available to download.
A key point is that there's no evidence the campaigns are doing it. It's a form of grassroots activism that exploits the unwillingness of social networks to do anything about their noise floor.
The BBC has some tips on How To Spot A Bot.
They often do not feature a profile image, and when they do it is often shared among multiple accounts – so watch out for duplicates.
Bots also tend to follow many more accounts than than they are followed by in turn – a sign that they do not have real friends or work colleagues.
They often have little to say apart from the topic of conversation they have been created to post about, and may tweet prolifically without apparent recourse to sleep.
Also watch out for accounts that reply to your messages in less time than was humanly possible to read what you wrote.
A final giveaway is if scrutiny of the bot's account reveals it has sent the same response to you to dozens of others too.