Cisco Systems announced on Monday that it has agreed to acquire a privately held developer of security technology for about $39 million in cash: Riverhead Networks, based in Cupertino, CA, employs 44 people. 

The deal for the shares of Riverhead it does not already own is expected to close in the quarter ending next month, Cisco says. The deal augments its current portfolio of security products and services.

Riverhead, founded in 2000, makes security technology that protects against denial of service attacks and other threats to corporate and telecommunications networks.