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What: Shares of Qualys (NASDAQ:QLYS) plunged by as much as 20% after the company reported earnings and offered disappointing guidance.

So what: Revenue during the fourth quarter came in at $24.7 million, with the 19% increase over last year being driven by increased subscription sales and cross-selling to existing customers. Non-GAAP net income was $2 million, or $0.06 per share. Both figures bested analyst forecasts, which called for $24.5 million in revenue and $0.05 per share in profit.

Now what: The current quarter's profit guidance left something to be desired, though. Qualys is expecting revenue in the range of $24.4 million to $24.9 million, while investors were expecting $25.3 million in sales in the first quarter. On a non-GAAP basis, the bottom line should be between a loss of $0.01 per share to a profit of $0.01 per share, which is short of the $0.04 profit investors were expecting. Full-year sales should be in the range of $106 million to $108 million.

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