Security experts acknowledge that organizations can get infected no matter how good their security controls are. Attackers use new delivery methods everything from social engineering to zero-day exploits and they often are effective. Traditional security solutions are built to be in front of what’s left of the perimeter to prevent infection attempts. Threat hunting requires a shift to a post-infection mentality and sets of tools such as SIEM (security incident and event management) and EDR (endpoint detection and response)
Source: https://thehackernews.com/2018/06/cyber-threat-hunting.html