The aim of the acquisition, Cisco officials said, is to allow the company to expand into a fast-growing segment of the web-based IT security market.
According to Cisco, the deal includes cash plus retention-based incentives and will close in the second quarter of next financial year.
ScanSafe, which is a privately held security company backed by investors Benchmark Capital and Scale Venture Partners, was founded in the late 1990s by Eldar and Roy Tuvey.
The Tuvey brothers - who have a 25% stake between them in ScanSafe - were the first IT professionals to come up with a secure web gateway service, since when other companies, notably MessageLabs, Webroot and Websense, have developed competing products and services.
Today, ScanSafe has offices in London and San Francisco, and has a wide range of alliance partnerships with AT&T, Google, Integralis, Kaspersky Lab, NEC, Orange and SoftScan.
Both brothers will remain with the company as it is integrated into Cisco, although no announcement on how the acquisition will affect jobs or distribution arrangements, has been made.