These are commonly used marketing terms, as you know, and I am not positive where they originate, but I can make a very good guess. Go back to early Western movies and you'll see where this comes from: the characters that had white hats were invariably the good guys, and the characters with black hats were the bad guys.

As film critic Roger Ebert notes in his review of the Western classic Shane: "Shane wears a white hat and Palance wears a black hat, but the buried psychology of this movie is a mottled, uneasy, fascinating gray."

Or the more pretentious Premier review of The Three Burials of Melquiades Estrada: "Three Burials is beautiful, authentic and brutally observant of human nature. With real Tex-Mex backdrops instead of the usual Monument Valley vistas and characters too complex to withstand simple white-hat/black-hat reductionism, Three Burials is a visionary portrait of the New West."

Back to the computer world. Free software guru Richard Stallman, in his book Free as in Freedom: Richard Stallman's Crusade for Free Software, notes: "The urge to confine the culture of computer hacking within the same ethical boundaries is well-meaning but impossible. Although most software hacks aspire to the same spirit of elegance and simplicity, the software medium offers less chance for reversibility. Dismantling a police cruiser is easy compared with dismantling an idea, especially an idea whose time has come. Hence the growing distinction between "black hat" and "white hat" -- i.e., hackers who turn new ideas toward destructive, malicious ends versus hackers who turn new ideas toward positive or, at the very least, informative ends."

In the marketing and search engine optimization sense, "white hat" techniques are those that are legit, aboveboard, ethical and honest, while "black hat" techniques are also known as dirty tricks, using techniques that are typically banned or prohibited by vendors or service providers.

Behind this all, however, is a troubling possibility that there's an element of racism involved with this nomenclature too. Why would "white" be good, positive and truthful, while "black" is bad, evil and unethical? Consider "white lies" as another example of this: hopefully that's not the etymological basis of this phrase, but it's something to think about when you talk about how you're a 'white hat marketer' or similar.

Hope this definition proves helpful to you!