The Nasdaq Composite Index headed for the biggest retreat in a month in afternoon trading today, dragged down by losses in Apple Inc. as a competitor introduced new smartphones and the company faced criticism for the theft of celebrity photos.

The Standard & Poor’s 500 Index fluctuated near a record. Apple, the world’s most valuable company, sank 3.3 percent for its biggest decline since January. Delta Air Lines Inc. lost 5.3 percent after it lowered forecasts for some third-quarter targets. PulteGroup Inc. fell 2.9 percent as homebuilders tumbled.

The Nasdaq Composite lost 0.4 percent at 2:18 p.m. in New York. Apple has the biggest weighting in the gauge at 8.7 percent. The S&P 500 rose less than 0.1 percent to 2,002.41, while the Dow Jones industrial average climbed 25.72 points, or 0.2 percent, to 17,093.28. Trading in S&P 500 stocks was 4.4 percent below the 30-day average at this time of day.

“Apple stock’s had a pretty strong move in the last several months,” Michael James, a Los Angeles-based managing director of equity trading at Wedbush Securities Inc., said in an interview. “A lot of positives from the iPhone launch are built into the stock price at these levels. People are merely taking profits.”

Apple had rallied in 15 of the previous 17 sessions, adding 9.3 percent since Aug. 7 to reach a record close of $103.30 Tuesday.

Samsung Electronics Co. unveiled a pair of Galaxy Note smartphones today, as the No. 1 seller tries to fend off Apple’s push into large-screen devices. The U.S. company yesterday said that a spate of nude photos from actresses including Jennifer Lawrence that were recently posted online were individually stolen from Apple accounts.

The theft, which prompted scrutiny from the U.S. Federal Bureau of Investigation, threatened to mar an Apple event on Sept. 9, where the company is set to unveil new iPhones, a wearable device and a mobile-payments system, people with knowledge of the matter have said.

Pacific Crest Securities LLC said it would likely cut Apple’s outperform rating unless the event shows “massive incremental profit opportunities.”

Apple led an S&P 500 index of technology stocks lower by 0.5 percent, the most among 10 main groups in the broader gauge.

The S&P 500 earlier climbed to an intraday record on reports that Russia President Vladimir Putin outlined a peace plan for Ukraine after agreeing with his counterpart Petro Poroshenko on steps toward a cease-fire in the conflict that has raged for more than five months.

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