Cisco is to buy IronPort Systems, a developer of email and web security products, for $830 million.

IronPort offers a range of appliances that enterprises use to protect their networks from Internet threats such as spam and spyware. Its appliances also help secure e-mail services for Internet service providers.

The acquisition, announced Thursday, will help Cisco address its customers' concerns about securing e-mail, messaging and other content as Internet threats continue to grow more sophisticated, Cisco said. The networking giant plans to integrate IronPort's e-mail and message protection technologies into its Self-Defending Network framework.

In addition to messaging security products, IronPort also sells a security management appliance that offers enterprises a single location to manage, store and monitor corporate policies.

IronPort, founded in 2000 and based in San Bruno, California, has 408 employees who will work as a business unit in Cisco's security and technology group. The deal is expected to close by July.

The acquisition follows several other smaller buys for Cisco during 2006, including Tivella, an IP video company, and Meetinghouse Data Communications, a wireless security vendor.