Key Highlights

● Fortinet collapsed to $139.10 on Thursday, October 29, after lowering its service outlook.

● Full-year service Revenue guidance was cut to $5.15 billion to $5.17 billion.

● Service revenue of $1.313 billion grew more slowly than analysts had expected.

● Palo Alto Networks, CrowdStrike and Zscaler fell without company-specific news.

Fortinet (NASDAQ:FTNT) lowered its service revenue outlook, sending the security software maker sharply lower on Thursday and dragging Palo Alto Networks (NASDAQ:PANW), CrowdStrike (NASDAQ:CRWD) and Zscaler (NASDAQ:ZS) down with it.

A headline beat with a hidden problem

On paper, Fortinet's third quarter looked fine. The network security company beat headline estimates after the bell on Wednesday and even raised its overall sales forecast. But investors zeroed in on the parts of the report that suggested slowing momentum, and on Thursday, October 29, the stock collapsed to $139.10, according to market data.

Product revenue of $765 million still grew quickly, but the pace slowed sharply from the prior quarter, one report said. Service revenue of $1.313 billion grew more slowly than analysts had expected. Non-GAAP gross Margin narrowed. Most important, Fortinet cut its full-year service revenue forecast to $5.15 billion to $5.17 billion.

Why service revenue matters so much

For security vendors, service revenue is the steady stream. It includes subscriptions for threat intelligence, support contracts and security updates that customers renew year after year. Investors typically value that recurring income more highly than one-off hardware sales because it is more predictable.

A cut to the service outlook therefore hits at the heart of how the market values a company like Fortinet. Analysts moved quickly. One brokerage downgraded the stock to Neutral with a $140 price target, while three other brokerages cut their targets, according to media reports. Market commentary framed part of the selloff as a "sell the news" reaction following the downgrade.

Contagion across the group

Fortinet's peers had no bad news of their own, but they fell anyway. Palo Alto Networks and CrowdStrike both dropped sharply in early trading, according to market data, which pointed to the Fortinet and ServiceNow (NYSE:NOW) selloffs and broader worries about AI disrupting software businesses. Another source showed Palo Alto still lower later in the session.

Zscaler opened at $235.51, well below its prior close of $255.80, before recovering to about $251.36, according to market data. No company-specific news was found for the stock.

The broader software sector was already under heavy pressure. ServiceNow plunged to its worst day on record after its own results, and the iShares Expanded Tech-Software ETF, IGV, slid hard, according to market data. Salesforce (NYSE:CRM) also fell.

The AI cloud over software

Thursday's software slump fed into a wider debate about artificial intelligence. Alphabet (NASDAQ:GOOGL)'s results revived concerns about mounting AI costs, according to media reports, and the Nasdaq Composite dropped 365.13 points to 26,184.72. For software companies, there is an added worry: that AI tools could change how businesses buy and use their products.

One market analyst said "markets are no longer rewarding companies simply for investing heavily in AI." In cybersecurity, the bar is being set by growth in recurring revenue, and Fortinet's report suggested that bar was not cleared.

A market that kept buying elsewhere

The software rout did not spread to the whole market. The Russell 2000 climbed 28.71 points to 2,859.22, and NYSE advancers outnumbered decliners by almost two to one. Investors were selling specific stories rather than stocks in general.

What to watch

The next tests for the group will be the remaining security and software Earnings reports in the weeks ahead, along with any follow-up commentary from analysts who cut targets. Investors will watch whether Palo Alto, CrowdStrike and Zscaler can recover their losses once the Fortinet shock fades, or whether Thursday marks a broader reset in how the market values recurring security revenue.