U.S. stock markets reeled today as the S&P 500 recorded its largest daily drop in over three months, plunging 1.6% amid a perfect storm of economic concerns.

Online posts show major price jumps at Walmart stores. One group is calling for a shopping "blackout" over broader concerns about profits, pricing, and fairness.

Amazon stock tumbled Friday after its Q2 cloud revenue growth disappointed compared to results from Google and Microsoft.

With these headwinds blowing in its face, Palo Alto's stock lost more than 5% of its value during the latter part of the trading day. That was a far steeper decline than the 0.4% slide of the ...