All sites on my server are experiencing login looping. Even wrong passwords do not elicit the red error message, simply reloads the login page. Same thing when I tried to install a new joomla site. The first page of the installation where it asks to select a language just keeps reloading.
Only one site had changes made, I installed several video extensions. Not sure if this was the cause or not. Doesn't appear to be hacking. Something just seems off.