This scam assumes you`re having an affair (so be careful if you really are)
(LA Times Latin America)

Call it the guilty-conscience scam. `I know about the secret you are keeping from your wife and everyone else,` the snail-mail letter begins. `More importantly, I have evidence of what you have been hiding.` It goes on to say `it is just your bad luck that I stumbled across your misadventures while...