There's something very _Snow Crash_ about this.

  assassins e_mail extortion hitmen scams spam terroristic_threats

Some call it spam, others call it laughable, but some people are very spooked about what you can find on someone with a simple Google search: E-mailed extortion threats demanding thousands of dollars to buy off a purported hitman with a contract. The scam goes down like this: J. Random Net.Scammer e-mails a likely target and claims to be an assassin that was paid to take them down. They're being kind enough to demand a couple of grand from them to not pull the trigger. Often the threats include some personal information, like the name of a spouse or children or a photograph of one's house (which you can pull off of the websites of county assessors' offices around the country without difficulty). If you try to get into it with the scammers, they might e-mail you back and try to scare you more.

Do yourselves a favour: Ignore them. If you're good at tracking down the senders of those messages, then you might want to consider doing so and contacting the ISPs of the senders (or the police local to the senders because technically this falls under the heading of 'terroristic threats').