Email spoofing is a technique used by hackers to fraudulently send email messages in which the sender address and other parts of the email header are altered to appear as though the email originated from a source other than its actual source. Hackers use this method to disguise the actual email address from which phishing and spam messages are sent and often use email spoofing in conjunction with Web page spoofing to trick users into providing personal and confidential information.
Software is usually used to collect or generate the email addresses that are spoofed. Hackers may create a virus that examines the contact information on an infected computer. That information is collected and sent to the hacker who then uses another piece of software -- a mass email program -- to send out bogus emails using the addresses collected.
Alternatively, hackers may use software that generates random email addresses to use to disguise the actual origin of the message being sent.