Recently, 430,000 email addresses and passwords were stolen, taken from the Yahoo Contributors Network. These email addresses were the addresses associated with a users Contributors Network account. The password as well. They are publicly viewable.
If you had an account on Yahoo Contributors Network, you should change your password for it and other services that you were using the same password for.
You can view the entire list here:
http://d33ds.co.nyud.net/archive/yahoo-disclosure.txt
(at the time of writing, they were using a mirror to hold the text file). Use the “Find” feature in your word processor to discover if your email address is contained with the 430,000 addresses. Mine was. Luckily, it was an older password that I no longer use.
Yahoo, interestingly, did not react to this leak quickly. I had emails from Hulu and Twitter before I had a single mention from Yahoo. Also, Yahoo did not require the compromised users to reset their passwords or even point them to a password changing link. I was surprised.
Of course, all of these email addresses had to pass through anti-spam mechanisms, meaning that most of these addresses and passwords were actually in use to some extent.
Outside resources:
Description of the issue from cnet: http://news.cnet.com/8301-1009_3-57471178-83/yahoos-password-leak-what-you-need-to-know-faq/ & http://news.cnet.com/8301-1009_3-57470786-83/hackers-post-450k-credentials-pilfered-from-yahoo/
