Four features of the new OS include advanced application controls, data leakage protection (DLP), WAN optimisation and SSL traffic inspection.
Most existing FortiGate customers with active maintenance contracts can upgrade to the new OS at no additional cost.
According to Charles Cote, regional director A/NZ Fortinet, businesses are saying they want to get more out of their existing IT investments, and looking for more with existing security budgets.
"FortiOS 4.0 is a simple firmware upgrade, which improves security for your applications and data, and makes it possible to speed up your applications and optimise your WAN," he said.