FireEye Inc., a brash cybersecurity startup that boasts of its unique defensive strategy, and industry pioneer Symantec Corp., whose Norton anti-virus programs sit on computers around the world, are on opposite poles of the information security industry. Their industry's customers are moving vital data to the cloud and exposing new Web vulnerabilities. Their adversaries are constantly evolving more insidious attacks. And so cybersecurity firms are forced to evolve on the run, as well, juggling precious dollars between research and marketing in search of a competitive edge, while skeptical customers wonder if the touted defenses will really work, analysts say. Both companies reported earnings this week, illustrating in different ways the harsh competitive pressures on the cybersecurity front.