Very little information was given about the bug, but the firm suggested users change their passwords immediately.
This was posted yesterday on the staff blog.
We have just released a very important security update for our iPhone and iPad apps addressing an issue that allowed passwords to be compromised in certain circumstances. Please download the update now.
If you’ve been using these apps, you should also update your password on Tumblr and anywhere else you may have been using the same password.
Please know that we take your security very seriously and are tremendously sorry for this lapse and inconvenience.
So change your password peeps!