Some 450,000 Yahoo users' email addresses and passwords have been leaked because of a security breach, the company confirmed Thursday, adding that just a small fraction of the stolen passwords were valid. The company said in a statement that an "old file" from the Yahoo Contributor Network was compromised Wednesday. Among the stolen emails and passwords were many from Yahoo's own email service along with those of other companies. The Yahoo Contributor Network is a content-sharing platform. Yahoo said it is fixing the vulnerability that led to the disclosure, changing the passwords of affected Yahoo users, and notifying other companies...