The last time Silicon Valley focused on cybersecurity was in the 1990s. That focus saw the emergence of two giants: McAfee and Symantec. The two companies remain the most recognizable household names, thanks to their traditional firewall and anti-virus products. Now they find the arena which they thought was their own encroached from two sides. On one side there are tech giants like Hewlett-Packard and Cisco Systems, which see new revenue opportunity in cybersecurity. On the other side there is a rush of start-ups backed by large investments of venture capital.