The scam is similar to the 19th Century Spanish Prisoner scenario, but has usually relied mainly on mail, faxes, and email as part of a multistage setup that targets people with enough money to supposedly help smuggle millions of dollars out of an African country, often Nigeria (hence the name). Those that take the bait and pay the (fake) transfer fees are promised exponential returns on their investments that never emerge.
There are scores of variations on the scam. For instance, a long-lost relative leaves a person a pile of money; to get the inheritance, the person needs to pay all the legal fees. But in general, most of these scams rely on greed to hook interest.
The message was addressed to around two dozen people. It’s unclear whether the hackers created their shortlist of targets using the communications history between my friend and her contacts or their geographic locations, but it seems likely given that other scams employ similar tactics. For example, hacked mailing lists from charitable organizations allow bad guys to set up fake charities and target the people most likely to donate based on past activity.
Finally, remember the fraudster is well trained and without a conscious. The most common form of getting to you is through Phishing. Which is convenient, in a way, as there are some practical steps you can take to avoid getting scammed.
Probably the most important is to maintain an online “stranger danger” mindset. If an email looks even the slightest bit suspicious, don’t open it. If it’s from someone you don’t know, don’t open it. If it says you’ve won the lottery, are being watched by some security agency, asks about an order (you did not make), or promises rewards in some other way, don’t open it. (Similar phishing attacks also appear on Facebook.)