A statement from Yahoo! confirms the Web giant has launched an investigation into last week’s claims that its system was breached exposing an estimated 450,000 user IDs.
D33DS, a hacking group, had reportedly claimed to be behind the attack.
U.S.-based data security firm Trustedsec stated the attack seemed to have originated from servers connected to a user-generated section of the site known as Yahoo Voices.
Yahoo! had earlier confirmed that an older file originating from Yahoo Contributor Network, which contained an estimated 450,000 Yahoo and other company users’ names and passwords, was compromised.
“Of these, less than 5 percent of the Yahoo accounts had valid passwords,” it said.
Yahoo! stated: “We are taking immediate action by 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.”
Trustedsec said it associated the compromised passwords with email addresses including from yahoo.com, aol.com and gmail.com.
The BBC had earlier reported that hackers used a technique called SQL injection to haul out the sensitive information from the database.
According to the U.S.-based security firm, the most alarming part was that the passwords stored were entirely unencrypted.
Encrypted passwords are not useable straight away, as the hackers need time to decode them.
Preliminary analysis by Imperva, a data security firm, suggested that the breached system might have also contained private data names, addresses, phone numbers and dates of birth.
