Every now and then everything is gone...
 

Sorry for the poor title, but don't know really how to describe it.

Every now and then, perhaps once every month, my forum restores itself to a previous stage, almost to the beginning when I created it. It's full of spam threads (which came before I took action), the style is back to standard and all threads posted after this date (months ago) are gone. The first time it happened I panicked, but I learned it usually takes a couple of hours and when I log back in, everything is back to normal again.

Any idea why this happens? If you need further details let me know.