By Benjamin Pimentel, MarketWatch

SAN FRANCISCO (MarketWatch) -- Shares of Autodesk Inc. plunged Friday, sustaining the worst drop within the S&P 500 index, after the software company's disappointing results left investors stunned.

The shares shed 14% to stand at $30.88.

Late Thursday, Autodesk (ADSK) missed revenue forecasts for the second quarter of fiscal 2013 and cut its outlook, in what Jefferies & Co. analyst Ross MacMillan called "a big step back."

"In a surprise to us, Autodesk missed Street revenues by 4%, blaming execution and soft demand," he wrote.

The decline set the tone for a downbeat session for the tech sector. The Nasdaq Composite Index (RIXF) shed a fraction to 3,047, leaving the benchmark on track to end the week in the red.

The S&P 500 (SPX) also was off a fraction, with tech losses also coming from Adobe Systems (ARUN), down 4%, and Netflix Inc. (NFLX), off 3%.

Salesforce.com (CRM) saw its shares slip a fraction, recovering from deeper losses, a day after the company posted a mixed business outlook.

On the upbeat side, shares of Aruba Networks (ARUN) jumped more than 17% after the networking company reported upbeat third-quarter results and issued a better-than-expected forecast.

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