To say that the Internet has had a profound impact on the world would be to understate its significance. There are more than 100 billion global search engine inquiries conducted each month, connecting people to new businesses and services, giving them access to information — and determining the next presidential election.

In a recent experiment, researchers took a diverse group of undecided voters, let them check out the candidates on Kadoodle (a specially designed search engine), and then counted the votes. They expected the search engine, which they’d rigged to give stories supporting certain candidates better rankings, to sway the choices of the voters, but not by as wide a margin as they discovered.

“I couldn’t even believe what we got,” said Robert Epstein, one of the American Institute for Behavioral Research and Technology’s senior research psychologist. “It seemed impossible … to be able to shift that many undecided voters toward whoever we chose.”

Some voters became 20% more likely to support the favored candidate, and almost none of them caught on to what was going on. Even those who did suss out the bias, according to researchers, felt even more validated that they’d made the right choice.

The “search engine manipulation effect,” which the series of studies being published in the Proceedings of the National Academy of Sciences explore, is nothing new. Search Engine Optimization (SEO) is a marketing strategy that aims to improve a business’s search engine ranking to expand its customer base. The more web traffic it gets, the more leads it can convince and convert into customers.

However, when search engines are the modi operandi of voters looking to learn more about a candidate, the “search engine manipulation effect” could prove to be worryingly influential. In a sense, all a candidate has to do to win an election is make sure he or she is dominating the search engine results pages. Epstein and fellow researcher Ronald E. Robertson have repeated the study’s results across five double-blind, randomized experiments that have analyzed the behavior of more than 4,500 undecided voters in the United States and India.

According to Epstein, the effect could put a staggering amount of influence into the hands of the largest search engines’ leaders. In the study, the researchers wrote that search engines have “perhaps already been affecting the outcomes of close elections.”

“We shouldn’t panic about these results, but we should be aware of them,” said Carleton University political-science professor Conrad Winn. “There are countless sources of information.”

Any factor that may have even the slightest of sway needs to be kept an eye on, as some elections come so close they actually have to be decided by a coin toss. Just this year, Prince Edward Island’s May provincial election in Vernon River-Stratford was literally decided by a coin toss. In 2010, the United Kingdom’s Michelle Gildernew beat Rodney Connor by just four votes.