In a recent blog post, Facebook (FB  ) warned ad buyers that Apple's (AAPL  ) recent privacy changes were limiting its ability to track the reach and clickability of their online ad campaigns.

"Our estimate is that in aggregate we are underreporting iOS web conversions by approximately 15%," wrote Graham Mudd, Facebook's VP of product marketing, in the post. Mudd said that underreporting was a common issue for a wide variety of advertisers. "We believe that real-world conversions, like sales and app installs, are higher than what is being reported for many advertisers," he continued.

Further along in the post, Mudd reiterated guidance, which Facebook gave during its earnings call in July, namely that the impact of Apple's privacy update would be more significant heading into the third quarter.

"We know many of you are experiencing this greater impact as we are," he wrote, assuring Facebook's ad-buyers. In the meantime, Mudd reiterated Facebook's multi-year commitment to developing new "privacy-enhancing technologies" aimed at enabling the funneling of highly personalized ads based on the smallest amount of personal data.

Mudd also stressed recent improvements to the company's conversion modeling methodology and other changes that have been in place since July. While at the same time, he urged companies to delay the evaluation of their ad campaigns, among other steps, in order to improve the accuracy of their analytics.

The blog post could be seen as a minor affront in Facebook's ongoing war with Apple over the future of what it calls "the free internet." The company's offensive dates back until at least December of last year, when it placed a series of full-page ads in a number of prominent broadsheets, including the Wall Street Journal and the New York Times.

Back then, as now, Facebook claimed that Apple's privacy changes would cause "the average small business advertiser stand to see a cut of over 60% in their sales for every dollar they spend."

"We're standing up to Apple for our small business customers and our communities," the ad concluded at the time.

It is worth mentioning that Facebook managed to bring in roughly $18 billion in additional ad spend over the first half of this year compared to the last, somewhat contradicting this dire narrative.

At the crux of the matter is the fact that Apple is a seller of devices and Facebook is a compiler of data. Apple has a vested interest in maintaining its reputation for privacy, and privacy has long been central to the company's ethos.

"We really just want to give users a choice," Craig Federighi, Apple's senior vice president of software engineering, said in an April interview. "These devices are so intimately a part of our lives and contain so much of what we're thinking and where we've been and who we've been with that users deserve and need control of that information."

Despite the glaring context of the blog post, Daniel Salmon, a research analyst at BMO Capital Markets, told the Wall Street Journal that it might be an effort on Facebook's part to temper expectations heading into quarterly earnings, due out in November.