U.S. property mogul Donald Trump gestures during a media event on the sand dunes of the Menie estate, the site for Trump's proposed golf resort, near Aberdeen, north east Scotland May 27, 2010. REUTERS/David Moir Donald Trump has quoted pro-Trump Twitter bots when tweeting messages to his supporters 150 times, according to an analysis of his account by SocialPuncher, a Russian social media company.

A Twitter "bot" is an automated (robot) account that is programmed to give observers the fake impression that it is operated by a human.

The other US presidential candidates — Ted Cruz, Bernie Sanders and Hillary Clinton — don't quote bots, SocialPuncher says.

The Trump campaign did not respond to multiple requests for comment from Business Insider.

It is not clear why these accounts exist. The bots make it appear that Trump's support on Twitter is bigger and louder than perhaps it is in real life. But Trump is so popular it's not clear whether the pro-Trump bot army actually makes any difference. And there is no evidence to suggest the Trump campaign knows about the bots. Trump sometimes uses interns to write his tweets for him, so perhaps they are making mistakes. Whatever the explanation, it seems that Trump is the only presidential candidate whose Twitter account has difficulty telling the difference between a bot and a human.

One potential explanation is that Trump's habit of retweeting anyone and anything — racists or Mussolini, for instance — has encouraged people to create dozens of bots that do little but target Trump with messages in the hope of getting a retweet. That might be a tactic to generate more followers for a bot network, because the more real followers a botnet has, the harder it is to detect. Usually, people create bots in order to inflate their follower count on Twitter, giving others a false impression of their importance. Twitter bans and deletes bots when it finds them.

But the real intention of the pro-Trump bot network is a mystery.

Trump has been caught quoting a bot before. Gawker created a bot that published Mussolini quotes on Twitter, and Trump approvingly cited it in February, apparently not realising that he was accidentally endorsing the Italian fascist dictator from World War 2.

But SocialPuncher founder Vlad Shevtsov claims that Trump's bot-quoting is on a far larger scale beyond that. He says:

In 2016 Donald Trump has quoted bot-accounts many times:

In January - 49 times

In February - 60 times

In March - 41 times.

A typical example, according to Shevstov, is @susanbirchfiel1, which appears to be the account of a "Happy Mother of 2 great boys." Trump quoted her in a tweet (he tends to quote tweets rather than actually retweet people) on March 30:

The interesting thing about this account, according to Shevstov, is that in a recent 40-day period it made 8,000 tweets and 10,000 likes, all of them pro-Trump. That's about 200 tweets and 250 likes per day — "definitely abnormal behavior for humans," Shevstov told Business Insider. We tweeted at the account and asked it to get in touch but did not hear back.

Another example is the account @Gearssuxs. The account was created in March 2013. For most of its life it was dormant. But between March 20 and March 30 of this year it made 1,150 tweets — an average of 115 tweets per day. Shevstov says that activity is "incredible" — and therefore likely to be automated.

Shevstov also highlights @Don_Vito_08. Trump quoted Don_Vito_08 on March 23:

Shevstov says that "@Don_Vito_08 is a classical bot - his twitter feed is a cocktail of @realDonaldTrump's retweets, @realDonaldTrum's news and tweets of @realDonaldTrump's bots." On April 6, for instance, the majority of @Don_Vito_08's tweets consisted of the same pro-Trump message tweeted over and over again, along with retweets of other pro-Trump messages. The account appears to have no other interests than Trump.

Shevstov says he has found about 150 pro-Trump accounts that behave like bots, endlessly tweeting and retweeting the same messages over and over again. Some of them have huge numbers of followers — but many of those followers appear to be fake or "empty" accounts.

Some of the accounts do have humans behind them, even though they often behave the way bots do. We contacted a handful of the alleged bot accounts to see if they would respond. Several did, and this one immediately denied, twice, that it was a bot:

The interesting thing about that denial is that I didn't ask @Gearssux if it was a bot or not:

So how did @Gearssux know I wanted to talk about bots before I asked the question? The account holder may have noticed that I had previously asked a different pro-Trump account why its followers looked like bots, and put two and two together:

Many of Cabot's 3.5 million followers look like this (below). The accounts don't have profile pictures, which is a common symptom of a bot network or a fake account (real people tend to show a picture):

The Cabot account declined to comment when contacted by Business Insider, saying it was "under contract no communications":

Some of the alleged bots appear to be occasionally tweeting as if they were controlled by a human, by responding to others' tweets or by making rare, non-Trump related comments.

Shevstov told Business Insider that he believes these are "troll" bots — accounts that mostly run as bots but that can be accessed by the humans controlling them, who tweet from them normally once in a while to maintain their human-like appearance. "All bots can be operated by a human, who can write from hundreds of accounts from tweet desk. It is a classic troll-factory."

Business Insider asked a separate social media analysis company, Socialbakers, to take an independent look at Shevstov's findings. Founder Jan Rezab told us that bots are increasingly sophisticated and can mimic human behaviour so closely that detecting them can be hard. He declined to comment further on the veracity of Shevstov's claims.

Trump is certainly followed by a large number of automated accounts. About 24% of Trump's 7.5 million followers are fake, according to TwitterAudit.com. That is not unusual. All large Twitter accounts attract fake followers. Hillary Clinton has a similar percentage of fakes, as does Business Insider. Bot networks often follow celebrities as a strategy to make them appear real, because Twitter has a policy of deleting bot accounts.

The only thing we can say for sure is that dozens of people have created tweetbots that simply tweet at Trump all day in the hopes he will retweet them.

And, it's working!