Yesterday the passwords for over 430,000 email accounts were leaked, with around 135,000 coming from Yahoo.com. However the rest were made up from Gmail, AOL, Hotmail, MSN and Comcast emails, meaning the vast majority of web based email users should give their account a check to make sure they weren't part of the leak.
While changing your password is just about the simplest way to avoid any problems associated with this - whether yours was revealed or not - security firm Sucuri has released a simple tool for checking whether your details appeared in the leak. All it requires is inputting your email address and it gives you a thumbs up or down.
Yahoo, affected most by the leak, has released a statement: "At Yahoo! we take security very seriously and invest heavily in protective measures to ensure the security of our users and their data across all our products. We confirm that an older file from Yahoo! Contributor Network (previously Associated Content) containing approximately 400,000 Yahoo! and other company users names and passwords was stolen yesterday,July 11. Of these, less than 5% of the Yahoo! accounts had valid passwords. We are fixing the vulnerability that led to the disclosure of this data, changing the passwords of the affected Yahoo! users and notifying the companies whose users accounts may have been compromised. We apologize to affected users. We encourage users to change their passwords on a regular basis and also familiarize themselves with our online safety tips at security.yahoo.com."