Investing.com – Facebook (NASDAQ:) and Alphabet (NASDAQ:) shares were under pressure in Friday’s premarket trading in a read across from Snap’s (NYSE:) badly-received third-quarter numbers late on Thursday.

Alphabet stock fell 1.8% and Facebook stock was 3.6% less. Snap’s market cap was much lower, and it plunged 20% before the markets.

Snap Thursday’s third-quarter revenue increased by 57% to $1.07 trillion, according to Snap. However this was less than anticipated and shows the potential dangers that Apple (NASDAQ)’s privacy rules can pose for apps that depend on advertising revenues.

Apple updated its privacy policy in the June quarter. It makes it more difficult for apps that track users to source data for ads targeting. To allow apps to track their users, they must opt in. It is now more difficult for advertisers to gauge the effectiveness and efficiency of ads-spend. Lacking adequate data means that companies will be reluctant to spend large sums of money advertising.

“While we anticipated some degree of business disruption, the new Apple-provided measurement solution did not scale as we had expected, making it more difficult for our advertising partners to measure and manage their ad campaigns for iOS,” CEO Evan Spiegel said.

While the company was aware of its impact, it did not publish its second-quarter results. The stock has held steady, supported by the belief that social media companies have been largely immune to supply chain disruptions, which have plagued both retailers and manufacturers over recent months.

Due to ongoing performance drags from privacy changes, the company stated that fourth-quarter revenues should average $1.18 billion.

Facebook has also warned that the rules could pose a problem for it and its advertisers, though comments by senior executives last month seem to have provided some support. Graham (NYSE.) Mudd is Vice President Marketing of the social media company. He stated that the company underestimates the effectiveness of advertising for Apple devices.