I have a Draytek 2860 and have turned on DOS Defense. Additionally Mail Alert has been activated. I seldom get any messages with tis setup.
Suddenly I have been drowned with messages of this kind:
2016/08/20 10:03:31 -- [DOS][Block][port_scan][188.8.131.52:5065->[snip my WAN address]:36097][UDP][HLen=20, TLen=538]
During one 24 hour period over 5000 were delivered with no let up in sight. So for the moment Mail Alert has been disabled and eventually the messages stopped coming. To me this is related to my DrayTEL account which is configured in my router. The VoIP service continues to work just fine.
Anyone with any ideas what this is all about?