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 computer security firm Sourcefire (Nasdaq: FIRE) are on fire today, soaring as much as 11.5% above last Friday's closing price.

So What: Last week's earnings report and timid guidance triggered a massive sell-off and today's bounce looks like an exuberant reaction to rumors that close competitor Fortinet (Nasdaq: FTNT) might be in buyout talks with IBM (NYSE: IBM). Riding through the ups and downs of this stock could give a hardened growth investor whiplash injuries.

Now What: This stock inspires lots of speculative trading, including 15% of the float being sold short at the latest reckoning, making it easy to swing hard in one direction or another. Getting back to the top will take some doing as Sourcefire still trades some 18% below last Monday's closing price. Closing that gap could be one more rumor away -- but the same is true for another huge drop, so tread here with caution.

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Fool contributor Anders Bylund holds no position in any of the companies discussed here. The Fool owns shares of International Business Machines. Try any of our Foolish newsletter services free for 30 days.We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool is investors writing for investors.