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What: Shares of Riverbed Technology (Nasdaq: RVBD) fell as much as 18% in early trading after competitor Silver Peak Systems issued a press release last night that stated it had counter-sued for patent infringement. Riverbed filed a claim against Silver Peak in June.

So what: Riverbed has since responded to the announcement, with general counsel Brett Nissenberg asserting in a press release that Silver Peak’s counter-claim is “without merit” and an “expected reaction” to Riverbed’s initial suit.

Now what: Investors don’t seem to be convinced. With the stock still off more than 15% as the closing bell approaches, they’re either afraid of Silver Peak’s counter, or nervous about lousy earnings reports from both Blue Coat Systems (Nasdaq: BCSI) and NetApp (Nasdaq: NTAP). Either way, it’s a tough day for those who own shares of Riverbed Technology. Where do you stand on this stock? Would you use the sell-off as a buying opportunity? Weigh in using the comments box below.

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Fool contributor Tim Beyers is a member of the Motley Fool Rule Breakers stock-picking team. He didn’t own shares in any of the companies mentioned in this article at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Google+ or Twitter, where he goes by @milehighfool. You can also get his insights delivered directly to your RSS reader.

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