Check and make sure your friend sent that great screensaver. A common method of transmitting malware is by infecting some unsuspecting user's computer and then using that computer to infect others. One simple way to do this is for a hacker to hijack your address book and send copies of the malware to everyone in that address book. Of course, YOU need to be enticed to run the malware, and the best way to do that is to fool you into thinking the attachment is something else. If a friend or acquaintance sends you a "great screensaver" or something like that, which you were not expecting, take a few minutes to confirm that person really sent it. If they know nothing about it, then delete the message."