Sonus ( SONSE) surged Monday as investors prepared for the troubled networking firm's latest financial update.

The stock jumped 12% after a Smith Barney Citigroup analyst boosted his rating to buy from hold. Analyst Alex Henderson said he expects the company's financial restatement process to yield only minor changes. The company is due to offer its latest update after the market closes Monday.

Sonus, based in Chelmsford, Mass., is working on a review of the last two years' financials. The company said three weeks ago that it had gotten a formal order of private investigation from the Securities and Exchange Commission. Sonus has said it is cooperating with the probe, which was triggered by the company's announcement in February that it was investigating its own books.

Sonus shares rose 47 cents to $4.27.

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