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

The group is considered kind of a black hat in the consulting business. 在咨询行业里，这个群体被看作是一群坏人。

In a dysfunctional organization, it is often impossible to tell who are wearing the black hats, and who are wearing the white hats. 在一个功能失调的组织中，往往分不清谁是坏人，谁是好人。

a hacker (= a person who gets into computer systems without permission) who does this for criminal or bad reasons

Black hats are highly motivated. There's a lot of money at stake. 黑客们积极性很高。这里面涉及到很多钱。