Opasa Worm - HTML/ZIP based attachments
This new worm is highly polymorphic and it's text resembles that of Bagle and Netsky. A possible message body could be:
"hi there! this important html messages cannot be represented as plain text and that's why i have sent it as compressed attachment! "
Attachment: An .html file with a random file name or a .zip archive containing the .html file. If the worm finds the WinZIP program on the infected computer, it will use it to compress the .html file.