Alphabet shares are at risk of posting their biggest-ever one-day drop after its earnings report, CNBC reported on Oct. 29 local time.

Alphabet shares fell more than 10 percent in premarket trading. Nasdaq futures also dropped sharply on the fallout.

Alphabet's third-quarter earnings per share and revenue both missed market expectations, the report said. CNBC said it was the first time both measures fell short at the same time since the fourth quarter of 2022.

A slowdown in the growth of its search business also stood out.

Investors have been concerned that AI chatbots and agents will increasingly take away Google search volume, CNBC said.

Google Search revenue missed expectations for a second consecutive quarter.

Microsoft was relatively better off. Its Azure cloud unit grew 48 percent in the latest quarter, becoming Microsoft's biggest business. Microsoft also gave a second-quarter revenue outlook of up to $97 billion, far above market expectations.

Microsoft lowered its annual capital spending guidance to $170 billion. The lower-than-expected capex was negative for AI-focused cloud companies, so-called neo-cloud firms. CoreWeave, Nebius and IREN shares were all weaker in premarket trading.

Cybersecurity stocks also dropped sharply in premarket trading. CrowdStrike and Palo Alto Networks fell more than 6 percent. Zscaler and Rubrik also slid by a similar amount.