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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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