FireEye, a Milpitas, Calif.-based network security firm, has acquired Mandiant for just over $1 billion in cash and stock.

The deal, which closed on Monday, wasn’t announced until Thursday on Mandiant’s website via a release. Alexandria, Va.-based Mandiant is the incident response and forensic firm that climbed in notoriety, both in and outside of the security space, with its in-depth report last February on the inner workings of a China-based cyber espionage group, dubbed “APT1,” targeting U.S. firms.

In January 2013, The New York Times, which employed Mandiant’s security services, also disclosed that its computer networks had been targeted by sophisticated hackers believed to be based in China.

With the acquisition, the two security firms aim to offer “the most complete library of actionable threat intelligence on advanced threats and a product suite that can apply that intelligence to detect and prevent attacks on both the network and endpoints,” the release from Mandiant said.

Kevin Mandia, Mandiant’s CEO prior to the deal, has now been appointed as senior vice president and chief operating officer of FireEye.

Under the terms of the acquisition, FireEye will pay out $106.5 million in net cash to Mandiant stakeholders. FireEye will also issue 21.5 million shares and options in the deal, worth about $900 million.