The Yamanner worm activates by just opening an infected e-mail message with Internet Explorer. To do this it uses a 0-day vulnerability in the Yahoo! Mail system. Yamanner builds its e-mail messages and sends them to the infected user's contacts. The sent e-mails look as follows:
Subject: New Graphic Site Body: Note: forwarded message attached.
The worm resides inside the e-mail body. It also tries to open a web page in another browser window.
