The counters that YouTube uses to register the number of views to reflect the success of the videos have inconsistencies, researchers have found.
This data can have economic implications, since with some online advertising campaigns that use videos, the portals can charge based on the number of registered views, researchers said.
One of the problems with the fraud that exists in this area is that of "bots", computer programmes that replicate the behaviour of an internet user, and which can therefore artificially increase the number of views, they said.
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"YouTube has a unique system for detecting fraud that is relatively efficient, but it has some inconsistencies," said Ruben Cuevas from Carlos III University Of Madrid in Spain.
Researchers discovered a discrepancy in the visit counts on YouTube.
"Specifically, it seems that there are visits that YouTube detects as fraudulent and, therefore, subtracts from the public views counter (the one that appears near the video), but at the same time Google charges the advertiser for them," said Cuevas.
"We have developed a more detailed study of YouTube's system for detecting false visits which, based on our results, is the most sophisticated one in existence," he said.
The method researchers used allowed them to play the role of all of the different agents involved in the fraud - the attacker, the poster of the video and the advertiser who pays to put ads in the videos.
"This allowed us to put our ads into videos that we posted on YouTube, and on which we carried out a fraudulent attack. That way, we could have a complete vision of the view count and of how those views were charged to the advertiser," said Cuevas.
With this method, when they sent "bots" to view two videos exactly 150 times. YouTube's public view counter only identified 25 views as real, researchers said.
However, Adwords, Google's main service for advertisers, charged the researchers for 91 of the views carried out by the "bots", they said.