Tumblr

In early 2013 the microblogging and social networking site Tumblr suffered a massive security breach that compromised approximately 65 million user accounts. The incident occurred prior to the acquisition by Yahoo but the data only surfaced for sale on dark web marketplaces years later. The stolen database contained user email addresses and passwords that were hashed using the SHA1 algorithm with salt. Security researchers noted that while salting provides some protection the age of the algorithm makes it vulnerable to modern cracking techniques. This breach remains one of the largest historical social media leaks impacting a significant portion of the platforms user base at that time.