Recently a couple of virus varients have been going around, using social networking as more effective ways of getting people to open them. There have been two iterations of them that I have seen so far.
The first purports to be from AirTran Airways, and the text thanks you for purchasing your ticket online through them, and indicates that a charge of $400+ has been made to your credit card. It also refers to the the attachment, which supposedly includes your receipt and the ticket. Of course, most people want to know what the hell is going on, since they didn't purchase any tickets online, and certainly not for $400+ dollars. Of course, they open the attachment, which isn't a receipt, but is in fact the virus. And the virus that has been going around does not seem to be stopped or detected by Symantec Antivirus, even using the most recent updates, so that machine in infected.
The latest varient arrives as a message from FedEx, warning either that the package that was sent to you, or that the package that you sent, was not able to be delivered because the wrong address was given. Again, an attachment with more information is included, and many people seem to want to open the attachment without thinking about it. The virus included in both of these messages seems to be a varient of the Virantex (or Braviax) trojan/virus, and is remarkably resistent to removal.
Please be careful. There is always lag between the newest virus varients showing up in the wild, and the latest updates released by Antivirus companies. There is always the chance that you can be infected, even if your virus definitions are up to date. Do NOT open any attachments that you aren't completely sure of. In fact, if you receive a message from someone that you DO know, with an attachment, contact them and confirm that they sent you the message, and that they included an attachment, before you open in, and go so far as to confirm the name of the attachment, as well.
Viruses have been out there for quite a while. Generally, they no longer carry destructive payloads, but they CAN slow your machine to a crawl, get you blacklisted when they try and spam other people with copies of themselves from your machine, or slam your network connection with extra traffic. And they can be VERY difficult to get rid of, once you're infected.