Source: FireEye.

What: Shares of FireEye (MNDT) fell more than 25% in Thursday's morning session, as investors were blindsided by a mixed third-quarter report with a side of horrible Q4 guidance.

So what: The network security specialist saw sales rising 45% year over year to $166 million. On the bottom line, FireEye reported a GAAP net loss of $0.88 per share, 6% worse than the year-ago performance.

Looking ahead, management slashed their full-year sales target from roughly $638 million to something like $624 million. If that 2% sales forecast doesn't look like much, the expected non-GAAP net loss per share more than doubled from $0.75 to $1.62.

Now what: Perhaps more damaging than a weak revenue forecast, FireEye also lowered its full-year billings target by 6%, indicating lower visibility in the quarters ahead. It's true that revenues are skyrocketing, but the moderated guidance may point to an approaching end of that hypergrowth curve.

Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

FireEye's report sent shockwaves across the data security industry. Barracuda Networks (NYSE: CUDA), which reported results nearly a month ago and had no other news on its plate today, fell as much as 6% on FireEye's report. A10 Networks (ATEN 0.70%), which bakes hacking safeguards into its high-speed networking software, fell more than 3% on an equally news-free day.

FireEye shares raced to a 71% year-to-date gain in June, but have now given back all of those rapid gains and much more. The stock is now down 29% so far in 2015, falling between A10's strength and Barracuda's even larger losses.