(Adds company's statement, analyst's comment and background; updates share movement)
Nov 8 (Reuters) - Affiliates of activist hedge fund Elliott Management Corp disclosed a stake of about 9 percent in Riverbed Technology Inc and said the network equipment maker was "significantly undervalued".
Riverbed shares jumped 15 percent on the Nasdaq on Friday.
Elliott Management is known for publicly agitating for a sale or a board shakeup in the companies in which it invests.
"This is a spark that could light a fire in Riverbed's shares," FBR Capital Markets analyst Daniel Ives said.
Riverbed, whose products boost data speeds on wide-area networks by up to 100 times, forecast current-quarter revenue below analysts' estimates last month because of a decline in sales to the U.S. government.
"Riverbed has been a very big underperformer since they acquired Opnet last year," Ives said.
Riverbed bought Opnet Technologies, which makes software to manage traffic on networks, for about $1 billion last October. Up to Thursday's close, the stock had fallen 23 percent since then.
Elliott Associates and its units, affiliates of the hedge fund founded and run by publicity-shy Paul Singer, said Riverbed should implement "value-maximizing operational, capital structure and strategic review initiatives".
In response, Riverbed said it was focused on creating value for its shareholders, and would continue to maintain an open dialogue with shareholders, including Elliott.
"The Goldilocks scenario is that Riverbed is eventually an acquisition candidate," Ives said.
Along with certain derivative agreements, Elliott said it had a combined economic exposure and voting power of about 10.4 percent in Riverbed.
Fidelity Management & Research Co was the largest shareholder in the company as of August, with a 12.5 percent stake.
Riverbed shares were up 15 percent at $17.43 in early afternoon trading.
(Reporting by Sruthi Ramakrishnan in Bangalore; Editing by Saumyadeb Chakrabarty)