I think that the most exploited vulnerability in Web3 is reentrancy. This type of cyberattack is older than Solidity itself, but it is technically in a completely different league than the other security problems in DeFi. If this topic is important to you and you want to know more about reentrancy attacks go here.
https://hacken.io/researches-and-investigations/black-box-vs-white-box-testing/Black box testing is when you have no idea how the software you are testing was programmed. This kind of testing is often done by testers who have little to no programming knowledge. It’s actually a good thing because they have the perspective of a usual end user. White box testing, also known as clear box testing, happens when you have insight into the code and/or general knowledge about the architecture of the software in question. It’s counted among low-level testing and focuses mainly on integration and unit testing.