Yaha.K is a mass mailing worm uses e-mail addresses stored in Windows Address book and also collects addresses from .ht* files to distribute infected messages. Yaha.K will also spread through the ICQ list, MSN Messenger list and Yahoo pager list.

Yaha.K arrives as an e-mail attachment with random message subject and message body. The SMTP server used to send the emails is chosen either from the registry or from the list inside the worm body.