Since the introduction of the ALLOWED_HOSTS setting in django 1.4.4, I get a lot of django error emails to my admin address for exceptions caused by some silly spider lookin
A bit of googling would have revealed that there's already a bug in Django's bug tracker for this:
https://code.djangoproject.com/ticket/19866
Until there is a fix in (hopefully) Django 1.5.1, there's a workaround involving a log filter.