Altor's software helps organisations control the security of information as it flows between servers and virtual machines on employee's desktop computers.
As organisations rely more on virtual servers for critical applications, concern around server security in the cloud has increased.
"This acquisition will extend our leadership in datacentre and cloud security and will enable customers to deploy a consistent set of security services across their physical and virtual infrastructure, while delivering lowest total cost of ownership," said Mark Bauhaus, Juniper's executive vice-president and general manager of service layer technologies.
Altor has led the virtualisation security market in innovation, defence-in-depth and performance, said Amir Ben-Efraim, chief executive and co-founder of Altor Networks.
"Today, we join forces with Juniper, which shares a common vision for securing data centers and the cloud, and together we look forward to extending our leadership in the VM security market," Amir Ben-Efraim said.
Altor Networks was founded in 2007 by security and networking experts from some of the industry's leading vendors. In early 2010, Juniper Networks made a venture investment in the company.
The purchase price does not include Altor shares already owned by Juniper.