According to the WSJ, citing sources familiar with the situation, large advertisers and sellers of advertising space are disappointed after learning that FB significantly overestimated the average duration of video viewing on its platform, in the last two years.

A few weeks ago, reports surfaced that the rate of content was artificially inflated because it took into account only those videos that have been viewed by more than three seconds. The company also announced that it is introducing a new calculation criteria, to solve this problem.

Directors of some companies, which Facebook has notified about the changes, requested more details on the calculations, the sources said.

It is thought that the previous method of calculation inflated figures by 60-80%.

The news is negative for Facebook, which is "praising" the rapid growth of "consumer" video through its platform in recent years.

FB shares fell in premarket trading to $ 126.92 (-2.43%).