I got an unexpected message, similar to maintenance mode at my site. As an admin i haven't done anything but the message displayed on the site for 10 mins. Is this is some kind of hacking or something else. As the effect of this, in assignments, all the submissions were visible to the students. Then i removed student from this permission from mod/assign:viewgrades to get it back.
The message was as follows:
<h2> our services aren't available right now</h2><p>we are trying to restore all services as soon as possible. please check back soon</p>ofF/bYAAAAACkKE12MK.............