Riverbed agreed Monday morning to be acquired by private equity firm Thoma Bravo for roughly $3.6 billion, or $21 per share.

That trumps the $19 per share that hedge fund Elliott Management had offered in January. The offer from Elliot, Riverbed's largest shareholder, was widely considered a tactic to push Riverbed into a sale.

Elliott Head of U.S. Equity Activism Jesse Cohn issued a very brief statement on the sale, saying that the hedge fund is "delighted with this outcome."

Elliott has ramped up investment in enterprise tech in the past year or so, using activist tactics to pressure tech companies for changes. Juniper has been one such target, with Elliott demanding a dividend and a paring-down of the product portfolio. CEO Shaygan Kheradpir was in the process of doing some of that before being ousted; new Juniper CEO Rami Rahim says he'll carry on with Kheradpir's policies.

Elliott also reportedly wants EMC to spin out VMware.

Riverbed's acquisition, due to close during the first half of 2015, would be the largest investment in Thoma Bravo's history. Jerry Kennelly would remain CEO of Riverbed. He's also chairman for the moment, but that seems unlikely to remain the case.

Riverbed's stock climbed to a peak of $22.28 in the weeks following the Elliott offer — suggesting that investors expected bigger offers to come — but it's languished since, closing at $18.74 on Friday.

Riverbed shares were up $1.54 (8.2%) at $20.28 in midday trading.