Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Lifelock Inc (NYSE:LOCK) weren't looking so safe today, falling as much as 10% and finishing down 8% after reporting first-quarter earnings last night.  

So what: It was by no means a terrible earnings report for the identity-theft protection service, as sales grew 31% in the quarter to $107.6 million, though the bottom line failed to keep up, holding at a loss of a penny per share, the same as a year ago. Still, both figures were ahead of analyst estimates at $105.6 million and -$0.02, respectively, and CEO Todd Davis said the company's "targeted marketing investments paid off' as it added its second-highest number of new members in the quarter. 

Now what: What seemed to cause the sell-off was weak bottom-line guidance for the current quarter as LifeLock sees a per-share profit of $0.03-$0.04 against estimates of $0.06. Still, full-year EPS guidance at $0.44-$0.48 was in line with the experts' projections at $0.45. Considering the lack of profit growth in the past quarter and weak EPS guidance for the second quarter, there may be some profitability concerns about LifeLock, but I'm willing to ignore those as long as full-year earnings remain on track. 

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Jeremy Bowman has no position in any stocks mentioned. The Motley Fool recommends LifeLock. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.