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What: Shares of ADTRAN (Nasdaq: ADTN) plunged today by as much as 11% after the company issued a warning on its third-quarter results.

So what: Revenue in the third quarter will be right around $162 million, with non-GAAP earnings per share between $0.18 and $0.19. Both of those figures are worse than expected because of the tough spending environment facing the company, as well as broader macro-economic concerns.

Now what: CEO Tom Stanton said the biggest challenge facing the company continues to be domestic wireless carriers that are delaying project rollouts as sales of legacy products dry up. Following the guidance revision, ADTRAN is facing a slew of analyst downgrades today, including from BofA/Merrill Lynch, which cut its rating from "buy" to "underperform" with a $15 price target. MKM Partners already rated the stock a "sell" but is reiterating that call and reducing its own price target from $18 to $14.

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Fool contributor Evan Niu holds no position in any company mentioned. Check out his holdings and a short bio. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. Try any of our Foolish newsletter services free for 30 days. The Motley Fool has a disclosure policy.