On Thursday, YHOO said that a third-party database was hacked, resulting in the release of an unknown number of usernames and account passwords. Yahoo Mail itself was not apparently compromised in the incident. Hackers who obtained the account data later attempted to use the data to access outgoing emails sent from compromised Yahoo Mail accounts, the Los Angeles Times notes.
Yahoo indicated that it is cooperating with law enforcement to identify those responsible for the Yahoo Mail hack. It has notified users of compromised Yahoo Mail accounts and has requested that they reset their passwords.
Last year, Yahoo overhauled its Yahoo Mail service, cleaning out old and inactive accounts. Yahoo Mail has about 273 million accounts.
Despite the news, YHOO stock gained slightly in Friday morning trading.