Email Spoofing !!!!

E-mail spoofing is a term used to describe fraudulent e-mail activity in which the sender address and other parts of the e-mail header are altered to appear as though the e-mail originated from a different source.Is a technique commonly used for spam e-mail and phishing to hide the origin of an e-mail message. By changing certain properties of the e-mail, such as the From, Return-Path and Reply-To fields (which can be found in the message header), ill-intentioned users can make the e-mail appear to be from someone other than the actual sender. The result is that, although the e-mail appears to come from the e-mail indicated in the "From" field (found in the e-mail headers) it actually comes from another e-mail address, probably the same one indicated in the "Reply To" field; if the initial e-mail is replied to, the delivery will be sent to the "Reply To" e-mail, that is, to the spammer's e-mail.
Method :- The technique is now used ubiquitously by mass-mailing worms as a means of concealing the origin of the propagation. On infection, worms such as ILOVEYOU, Klez and Sober will often try to perform searches for e-mail addresses within the address book of a mail client, and use those addresses in the From field of e-mails that they send, so that these e-mails appear to have been sent by the third party. For example: User1 is sent an infected e-mail and then the e-mail is opened, triggering propagation The worm finds the addresses of User2 and User3 within the address book of User1 From the computer of User1, the worm sends an infected e-mail to User2, but the e-mail appears to have been sent from User3 .