Mail

The mail worm is the simplest type of worm. It's primary mode of propagation is through social engineering. By sending large quantities of mail with content that deceives people and/or triggers their curiosity, recipients are tricked into running an attached program. Once executed, the program will send out copies of itself via email to recipients found in the victims address book. This type of worm is usually stopped quickly when antivirus companies update their signature files, and mail servers running those AV products start filtering the worm mails out. Users, in general, are becoming more and more aware of this type of malware, and many won't run attachments sent in mail anymore. Regardless, this method of infection still manages to be successful.