Refers to an ethical hacker who tests security with permission, as opposed to a malicious black hat hacker. Used in IT security contexts.
He performs security assessments for companies as a white hat hacker.
Variant spelling with an interpunct; less common but still seen.
Borrowed from English 'white hat', originally from Western films where the hero wore a white hat. In computing, it contrasts with 'black hat' for malicious hackers.