Recently I have been getting a number of spam email messages that don't quite look like your average spam. If someone that you know has there email get 'hacked', then you might start getting messages from them that they didn't send. Eventually you will most likely get a warning from them alerting you to this.
The ones that I have been seeing are a little different. They say that they are from someone that you know, but if you look carefully you will see that the email address that it is displaying isn't theirs. For example, the message may say it is from 'Jim Santos', but the email address that it says goes along with that name is 'email@example.com'. As soon as you see such a mismatch, delete the message. It may or may not be infected, but it is almost definitely spam.