It has been a difficult year for Facebook and now the social media giant finds itself accused of deliberately misleading advertisers for more than a year over how it measured viewership of video ads.

A group of small advertisers, including online marketing agency Crowd Siren, have filed an amended complaint with a court in California, alleging that Facebook knew of irregularities with its video metrics as long ago as 2015 but failed to disclose the information for more than a year, the Wall Street Journal reported.

The Journal was the first to report the problem in September 2016, claiming that Facebook overestimated the average time users spent viewing paid video by 60% to 80%, and Facebook apologised at the time promising that the error had been fixed.

Crowd Siren and a handful of other advertisers sued over these mistaken metrics, but they have now amended their lawsuit having reviewed 80,000 pages of internal Facebook documents.

They now allege that the scale of the miscalculation was much worse than understood in 2016 and that paid video ad metrics were inflated by 150% to 900%.

What’s more, the plaintiffs allege that Facebook took no corrective action for more than a year and also adopted a “no PR” policy to avoid drawing attention to the matter.

“Facebook’s internal efforts behind the scenes reflect a company mentality of reckless indifference toward the accuracy of its metrics,” they said in their filing.

However, Facebook strenuously denied the claims, with a spokesperson describing the lawsuit as “without merit” and that the company has filed a motion to dismiss these claims of fraud.

“Suggestions that we in any way tried to hide this issue from our partners are false. We told our customers about the error when we discovered it – and updated our help center to explain the issue,” the company said.

Sourced from Wall Street Journal; additional content by WARC staff