There is a very common scam going around right now in which someone somehow gains access to a valid password, and then tries to blackmail you. The message typically state that you've been caught on a porn site, and the sender will claim they have explicit video of you. There is another one in which the sender claims the person has been having an affair and has been caught, and all the information will be sent to his friends and family. This has happened to multiple people in my office as well. There are sites on which passwords are listed - they're been captured in one way or another. Do not send money, but do change your passwords anywhere that you might have used that password. They have nothing on you, they're just hoping to get the right guilty person who will send the money.