Email-Worms spread via email. The worm sends a copy of itself as an attachment to an email message or a link to its file on a network resource (e.g. a URL to an infected file on a compromised website or a hacker-owned website).
In the first case, the worm code activates when the infected attachment is opened (launched). In the second case, the code is activated when the link to the infected file is opened. In both case, the result is the same: the worm code is activated.
Email-Worms use a range of methods to send infected emails. The most common are:
- using a direct connection to a SMTP server using the email directory built into the worm’s code
- using MS Outlook services
- using Windows MAPI functions.
Email-Worms use a number of different sources to find email addresses to which infected emails will be sent:
- the address book in MS Outlook
- a WAB address database
- .txt files stored on the hard drive: the worm can identify which strings in text files are email addresses
- emails in the inbox (some Email-Worms even “reply” to emails found in the inbox)
Many Email-Worms use more than one of the sources listed above. There are also other sources of email addresses, such as address books associated with web-based email services.