A niggahnaut is an internet surfer whose only, or main, purpose in life is to solicit other netizens via IMs and e-mails for various online scams, most notably the infamous Nigerian 419 scam. The suffix " -naut" in "Niggahnaut", just like "internaut", "argonaut", "astronaut" and "cosmonaut", is derived from the Greek word "nautis" = sailor.
A niggahnaut does not necessarily have to be black, or even African. Niggahnauts send their scam e-mails and IMs from all over the globe, i.e., North Africa, the Middle East, Pacific Asia, Brasil, the USA, Australia, the UK, etc. However, by far, most niggahnauts reside in, and their scam messages and IMs originate from, West Africa, most notably Nigeria, Ghana, Ivory Coast and Sierra Leone.
One needs to be on the lookout for differentiated scams and evolving scamming techniques. Some niggahnauts have noticed, for example, that westerners may not respond positively to IMs seemingly from an African female, so they switched her "location" to the USA, the UK or a country where large numbers of Africans or people of African descent may reside.
To further improve their response rate, some niggahnauts decided to employ fake profiles of "white" women instead of say, African-Americans. They dropped the ball, of course, when in their fake Yahoo! profiles they named or nicknamed their bogus white female characters as "Queen" or a similar, African-sounding name.
I have been receiving lots of Nigerian 419 SPAM from niggahnauts lately.