Nielsen, the company responsible for measuring television viewership across the globe, announced on Friday that its ratings have been a little off since this spring, due to a technical error.

“The technical error was introduced on March 2, 2014, and was generally imperceptible until we saw high viewing levels associated with fall season-premiere week,” the company said in a statement. “As a result, small amounts of viewing for some national broadcast networks and syndicators were misattributed.”

According to Deadline, ABC’s fast nationals – the preliminary ratings before the full national ratings are released several hours later – were inflated for the 18-49 demographic for the first nine nights: 20 programs saw a lift in ratings without a single downward adjustment. By comparison, during that same period the three other major networks -- NBC, CBS and Fox -- experienced a combined 15 adjustments.

Nielsen said the problem was uncovered on Oct. 6. A software fix corrected the glitch on Oct. 9. The company says all data released Friday and going forward will be accurate. In addition, the company also said it will reprocess data dating back to Aug. 18, when the first new season of broadcast network programing aired. That data is expected to be reissued Oct. 31.

While the bug affected only 0.1 percent - 0.25 percent of all viewing minutes, the gaff is considered huge for the company that advertisers and networks rely on so heavily, Capital New York reports.

“We are working closely with our clients to manage this situation and will continue to be transparent with the industry and the media about our plans,” the company said in the statement. “In addition, we will undertake an exhaustive postmortem—internally and with our clients—and we are asking the MRC to join us in these efforts.”

This isn’t the first time Nielsen has run into problems with its reporting. In 2012, leading news broadcaster New Delhi Television Ltd. filed a lawsuit in New York against Nielsen seeking $1 billion in damages for allegedly manipulating Indian TV viewership data for almost a decade. In March, according to the Hollywood Reporter, a New York lower court ruled the case should be heard in India. NDTV plans to appeal.

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