an alert on my FRITZ!Box 7390: "internet: Bonk Attack detected"

I found this message today in my telnet session on my FRITZ!Box:

Nov 26 10:16:25 dsld[2178]: internet: Bonk Attack detected (1)

I think, this I saw this already a couple of months ago, and I think, the box rebooted then, but it didn't do that no.