On May 12, the microblogging website Tumblr notified users of a data breach that occurred in 2013. The company had kept quiet about the number of site users that were affected, although it has since emerged that 65 million account credentials were stolen in the Tumblr data breach. Stolen email addresses and passwords were recently offered for sale on a Darknet marketplace called TheRealDeal.

Tumblr Data Breach Ranks as One of the 5 Biggest Data Breaches of All Time

The massive Tumblr data breach may not be the largest ever discovered, but it certainly ranks as one of the biggest, behind the breach of 360 million MySpace account details, the theft of 164-million LinkedIn account credentials, and the 152 million-record Adobe breach. All of these huge data breaches occurred in 2013 with the exception of the LinkedIn breach, which happened a year earlier.

These breaches have something else in common. They were all discovered recently and the stolen data from all four data breaches have been listed for sale on illegal Darknet marketplaces by the same individual: A Russian hacker with the account “peace_of_mind” – more commonly known as “Peace”. It is not clear whether this individual is responsible for all four of these data breaches, but he/she appears to have now obtained all of the data.

The person responsible for the theft appears to have been sitting on the data for some time as according to Tumblr, as the login credentials do not appear to have been used.

Fortunately, the passwords were salted and hashed. Unfortunately, it would appear that the SHA1 hashing algorithm was used, which is not as secure as the latest algorithms. This means that hackers could potentially crack the passwords. The passwords were also salted so this offers more protection for individuals affected by the Tumblr data breach. However, as a precaution, site users who joined the website in 2013 or earlier should login and change their passwords.

Do You Reuse Passwords on Multiple Sites?

Even if victims of the Tumblr data breach have changed their password on the site before 2013, they may still be at risk of having their online accounts compromised if their password has been used for multiple online accounts.

If you have been affected by the Adobe, LinkedIn, MySpace, or Tumblr data breach, and there is a possibility that you have reused passwords on any on other platforms it is strongly advisable to change all of your passwords.

Peace may not be the only individual currently in possession of the data, and it is highly unlikely that the data will only be sold to one individual.

If you are unsure if your login credentials have been compromised, you can check by entering your email address or username on haveibeenpwned.com