A list of 450,000 usernames and passwords from Yahoo's "Contributor Network" has been posted on the Internet. The passwords were not encrypted. Yahoo has confirmed that usernames and passwords were compromised. An analysis of the data by a security site determined that the list also contains username and passwords for other online services.
What should you do? Change your Yahoo password, even if you haven't used their "Contributor Network." In addition, change your password on other online services such as Google or Facebook. If you use the same passwords on other sites, change them too.