You might’ve gotten that “Security Warning”, or heard people talking about getting them, or losing their accounts. Some people say it’s because of browser extensions like Missing E or XKit.
Again, let me clarify that these warnings are not because of XKit or Missing E, and nobody actually got their account deleted by Tumblr itself. Some people just like drama.
First of all, Tumblr does not delete accounts for merely using a browser extension.
You can read more about it here. I’ve written so much about this in the past, so I won’t get into detail. Long story short: your account will not get deleted because of XKit, Tumblr Savior, Missing E or Tumblr Life.
Secondly, there seems to be a security breach on Tumblr’s servers. That is why you are getting those security warning messages.
It seems that someone found a way to gain access to accounts via usage of cookies. You can read more about it on MSNBC. A more technical story is available on Softpedia.
Some peoples accounts might’ve gotten deleted after being hijacked.
Unfortunately, Tumblr staff chose to be completely silent about this, so we don’t know when this is going to be fixed, nor how many accounts were “hijacked.”
I highly recommend changing your account password, even though you did not get the warning message. And try not visiting “strange looking” blogs for a while, since they might’ve been “infected.”
Thank you for your time, and thank you for using XKit.