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 16% to stand at $30.14.

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.

Despite the decline, the tech sector managed to bounce back from early losses. The Nasdaq Composite Index (RIXF) was last up a fraction at 3,066, although the benchmark was on track to end the week in the red.

The S&P 500 (SPX) also gained a fraction.

Among the notable gainers were shares of Aruba Networks Inc. (ARUN) which jumped 17% after the networking company reported upbeat third-quarter results and issued a better-than-expected forecast.

Also on the rise were shares of Amazon.com Inc. (AMZN) which were up more than 2% at $246.60. The company announced an "expanded licensing agreement" with NBC Universal which would allow the online retailer to offer more online video content.

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