Security is not just like paint: it can’t just be applied after a system has been completed. The standard approach to flushing out design and implementation defects is testing. But how can we know the security stance of software today, with practical methods? Security conscious developers are increasingly turning to a new approach: formal methods (FM) The roots of formal methods lie in the 1970s, and recent years have seen rapid adoption of FM technologies. Modern FM tools have been refined by global-scale companies like Microsoft, Facebook, and Amazon.
Source: https://www.helpnetsecurity.com/2021/01/04/formal-methods-software-security/