someone in a particular situation who is acting for morally good reasons, or something that shows who this person is

We work for the good guys. We're the white hats. 我们为好人工作。我们是好人。

It would be simpler if some of us had white hats and some of us had black hats, but in fact things are more complicated than that. 如果人们仅仅以白帽好人、黑帽坏人相区分的话，就会很简单，但事实上，事情要比这复杂得多。

a hacker (= a person who gets into computer systems without permission) who has morally good reasons for doing this

Levy is a so-called "white hat" computer hacker who hunts for computer security flaws to help repair them. 利维是一个所谓的“白帽”电脑黑客，他搜寻电脑安全漏洞以帮助修复漏洞。