Usernames and passwords of some of
Yahoo's email customers have been stolen and used to gather personal
information about people those Yahoo mail users have recently corresponded
with, the company said Thursday.
Yahoo didn't say how many accounts
have been affected. Yahoo is the second-largest email service worldwide, after
Google's Gmail, according to the research firm comScore. There are 273 million
Yahoo mail accounts worldwide.
It's the latest in a string of
security breaches that have allowed hackers to nab personal information using
software that analysts say is ever more sophisticated. Up to 70 million
customers of Target stores had their personal information and credit and debit
card numbers compromised late last year, and Neiman Marcus was the victim of a
similar breach in December.
"It's an old trend, but it's
much more exaggerated now because the programs the bad guys use are much more
sophisticated now," says Avivah Litan, a security analyst at the
technology research firm Gartner. "We're clearly under attack."
Yahoo Inc. said in a blog post on
its breach that "The information sought in the attack seems to be names
and email addresses from the affected accounts' most recent sent emails."
That could mean hackers were looking
for additional email addresses to send spam or scam messages. By grabbing real
names from those sent folders, hackers could try to make bogus messages appear
more legitimate to recipients.
"It's much more likely that I'd
click on something from you if we email all the time," says Richard
Mogull, analyst and CEO of Securois, a security research and advisory firm.
The bigger danger: access to email
accounts could lead to more serious breaches involving banking and shopping
sites. That's because many people reuse passwords across many sites, and also
because many sites use email to reset passwords. Hackers could try logging in
to such a site with the Yahoo email address, for instance, and ask that a
password reminder be sent by email.
Litan said hackers appear to be
"trying to collect as much information as they can on people. Putting all
this stuff together makes it easier to steal somebody's identity."
Yahoo said the usernames and
passwords weren't collected from its own systems, but from a third-party
database.
Because so many people use the same
passwords across multiple sites, it's possible hackers broke in to some service
that lets people use email addresses as their usernames. The hackers could have
grabbed passwords stored at that service, filtered out the accounts with Yahoo
addresses and used that information to log in to Yahoo's mail systems, said
Johannes Ullrich, dean of research at the SANS Institute, a group devoted to
security research and education.
The breach is the second mishap for
Yahoo's mail service in two months. In December, the service suffered a
multi-day outage that prompted Yahoo CEO Marissa Mayer to issue an apology.
Yahoo said it is resetting passwords
on affected accounts and has "implemented additional measures" to
block further attacks. The company would not comment beyond the information in
its blog post. It said it is working with federal law enforcement.
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