In early 2013, Tumblr suffered a data breach that resulted in the exposure of over 65 million accounts.
The data was later put up for sale on a dark market website and included email addresses and passwords stored as salted SHA1 hashes.
Source: https://haveibeenpwned.com/PwnedWebsites#JukinMedia
"id": "TUM114441222",
"linkid": "tumblr",
"type": "Data Leak",
"date": "02/2013",
"severity": "85",
"impact": "3",
"explanation": "Attack with significant impact with internal employee data leaks"