Yahoo hack – a billion reasons to change your email account

Oops, it happened again. And I did a YouTube live stream for the first time.

Graham Cluley
Graham Cluley
@[email protected]

Yahoo billion

At one billion records, it’s the biggest data breach ever.

Just a few months after Yahoo announced that hackers had stolen 500 million account details during a 2014 data breach, the troubled company is back with more bad news:

Law enforcement provided Yahoo in November 2016 with data files that a third party claimed was Yahoo user data. We analyzed this data with the assistance of outside forensic experts and found that it appears to be Yahoo user data. Based on further analysis of this data by the forensic experts, we believe an unauthorized third party, in August 2013, stole data associated with more than one billion user accounts. Yahoo has not been able to identify the intrusion associated with this theft. We believe this incident is likely distinct from the incident we disclosed on September 22, 2016. We are notifying potentially affected users and have taken steps to secure their accounts, including requiring users to change their passwords. Yahoo has also invalidated unencrypted security questions and answers so that they cannot be used to access an account.

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Separately, our outside forensic experts have been investigating the creation of forged cookies that could allow an intruder to access users’ accounts without a password. Based on the ongoing investigation, the outside forensic experts have identified user accounts for which they believe forged cookies were taken or used in 2015 or 2016. The company is notifying the affected account holders, and has invalidated the forged cookies. We have connected some of this activity to the same state-sponsored actor believed to be responsible for the data theft we disclosed on September 22, 2016.

Yep, last time it was 500 million account details breached. Now Yahoo says that in August 2013, in what appears to have been a separate security incident, the details of one billion accounts (that’s an awful lot of zeroes) was accessed by hackers.

The stolen information included names, email addresses, telephone numbers, dates of birth, hashed passwords (using MD5) and, in some cases, encrypted or unencrypted security questions and answers. No payment data was accessed.

As the news broke around the world (late in the evening here in the UK), I started my first ever YouTube live stream to discuss what appeared to have happened and answer questions.

One BILLION Yahoo users put at risk after hack - LIVE STREAM

It’s horrendous news for Yahoo, which is trying to sell itself to Verizon. But it’s even worse for the innocent users and companiesd whose information has been exposed as a result of this hack.

Yahoo’s security chief Bob Lord posted that hackers are thought to have created forged cookies that could permit access to users’ accounts without any password whatsoever.

Let that sink in for a moment. Malicious hackers have been able to break into Yahoo accounts since 2013, without any password.

As I describe in the video, if you are at risk you should ensure that:

  • change your Yahoo password (make it strong and hard to crack).
  • you are not using the same exposed password anywhere else on the internet. You should *never* re-use passwords.
  • change your security questions & answers (get into the habit of lying in your security answers, so rather than using something easy to determine like your real mother’s maiden name you choose something random like “UkCWm6)7.u74cu93YpR;” instead).
  • use a password manager to remember what your passwords are, as well as your security answers.
  • Watch out for phishing emails that pretend to come from Yahoo.
  • enable two-step verification or two-factor authentication on your accounts, where available.

Incidents like this don’t do any good at all for Yahoo’s tarnished brand. You may want to consider switching your email account to somewhere else if you’ve lost trust in the company.

I’m afraid I just wouldn’t trust Yahoo anymore, and can’t recommend them to my friends and family.

Check out the Yahoo FAQ for more details and advice.

Further reading: How to delete your Yahoo account.

Graham Cluley is an award-winning keynote speaker who has given presentations around the world about cybersecurity, hackers, and online privacy. A veteran of the computer security industry since the early 1990s, he wrote the first ever version of Dr Solomon's Anti-Virus Toolkit for Windows, makes regular media appearances, and is the co-host of the popular "Smashing Security" podcast. Follow him on Twitter, Mastodon, Threads, Bluesky, or drop him an email.

7 comments on “Yahoo hack – a billion reasons to change your email account”

  1. Chris

    What's so maddening about this *isn't* the abysmal security practices that are – or certainly were – the standard at Yahoo. It's not the fact that their IDS, if it even existed, couldn't pick up the exfiltration of a *billion* records, although that's surprising enough. It's the pathetic way that the company ignored the issue, repeatedly trying to sweep it under the carpet. It shows utter contempt for their user base.

    Only now, while trying to extract some coin out of Verizon, have they reluctantly owned up to this, while untold amounts of personal and financial damage could have been wrought for years. Though it's sad for the hardworking employees there who haven't yet jumped ship, I can see this sinking Yahoo as a company – and frankly would welcome that news.

    1. Simon · in reply to Chris

      It's amazing that such a company that once passed up buying Google is now in such a mismanaged (Marissa), reckless (multiple data breaches) and redundant state (pointless and wasted acquisitions).

      Verizon is the vulture that'll be pecking at the carcass of Yahoo for any IP, telemetry and profiling data from it's remaining user base.

  2. graeme

    Do we know if the passwords were salted before hashing – if not, then can we assume they have been reverse engineered using rainbow tables and the like, which raises the stakes a little for those that use their passwords elsewhere or use simple pattern to create them.

    1. Graham CluleyGraham Cluley · in reply to graeme

      Worryingly, Yahoo doesn't mention that the password hashes were salted. You have to think that if they were salted, they would have mentioned that they were salted. After all, that's the kind of question a security wonk would ask — and surely Yahoo's CISO would have wanted that information to be included in the statement.

      Furthermore, it appears that Yahoo was using MD5 rather than the stronger bcrypt algorithm. Another reason to worry.

      Some discussion of these points on The Register:

  3. Blair S.

    I was one of those hacked. I did some research after discovering this (in 2013) and found this:

    To this day spam is still being sent to all the contacts in my stolen Yahoo email address book (a few of which were mine).

  4. A. Schmidt

    This is the kind of news that makes me happy that I only use Yahoo mail for getting posts from mailing lists, that the password I use is unique to them, and I signed up using fake info. Otherwise, I might be worried.

  5. RichM

    I have a BT broadband contract which provides me with BT Yahoo mail account. I have been looking at the security on this account and note that BT does not provide access to some of Yahoo's security features such as recent login activity. I am very annoyed that I may have to move away from this email account.

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