It is always after the security breach happens when a businesses learns that their firewall and anti-virus solution had an unprotected flaw – the flaw that became an adversary’s attack vector. Can you ever have confidence in network security and protection measures? Is it possible to know you have a defensive watch over everything?
For certain, the work of network remediation after an attack has occurred is extremely hard. It is the job of working in the dark when layered security architecture is not in place. But if this is your situation, the following link is the general path for how to approach it: