More than a third of both presidential candidates' Twitter followers are bots, study finds

Donald Trump has routinely bragged about his nearly 12 million Twitter followers on the campaign trail.

But that number may actually be a bit misleading, according to a new study by digital ad firm eZanga, which looked at how much digital marketing money campaigns are wasting showing ads to automated bots that mimic human behavior.

The firm found that more than than one third of the Twitter accounts that follow the candidates of both major parties are not human -- 39 percent, or 4.3 million, in the GOP nominee's case and 37 percent, or 3.1 million of Democratic nominee Hillary Clinton's Twitter audience.

By comparison, the White House's official @POTUS account is followed by about 29 percent, or 3 million, fake accounts.

The findings could reveal a blindspot in advertising strategies as both candidates gear up their digital marketing spend leading into the final stretch of the campaign cycle.

While Trump has eschewed most forms of traditional advertising for much of his run, he has, at times, outspent his opponent on digital ads, including sponsored hashtags with a six-figure price tag as well as other Twitter campaigns.

A report last year from research firm Borrell and Associates projected that candidates and their affiliate groups would spend record amounts on online ads this election cycle.

Mobile advertising fraud in general has become a big problem for the industry as increasingly bigger portions of ad budgets are dedicated to reaching people on their smartphones. Oftentimes, these bots are part of larger fake traffic schemes set up to drain money from advertisers with fraudulent numbers.

In any case, the spread of shell Twitter accounts make candidates at least think twice before spending big on digital marketing on the platform.