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 Riverbed Technology, (UNKNOWN:RVBD.DL) jumped 16% Friday after activist investor Elliot Associates disclosed it has obtained a 9% stake in the wide area network specialist and will push it to find ways to increase shareholder value.

So what: Specifically, Elliot Associates stated it believes Riverbed Technology stock is "significantly undervalued," especially considering Riverbed possesses "extremely loyal customers" and "occupies a mission-critical position in thousands of networks." What's more, Elliot believes Riverbed should implement a strategic review to decide how to best optimize its operations and capital structure in a way that maximize shareholder returns.

Now what: Riverbed Technology, for its part, elaborated further in a subsequent SEC Filing, saying "Elliott believes that these initiatives will prudently, but significantly, provide a meaningful increase to the company's valuation. We have detailed these observations to the Board of Directors of [Riverbed] and look forward to a constructive dialogue."