It’s not often that a zero-day vulnerability causes a network security vendor to urge customers to physically remove and decommission an entire line of affected hardware — as opposed to just applying software updates. But experts say that is exactly what transpired this week with Barracuda Networks, as the company struggled to combat a sprawling malware threat which appears to have undermined its email security appliances in such a fundamental way that they can no longer be safely updated with software fixes.