Whack a mole is a fun isp game as ip ranges stay the same and users may be rotated so blocking one troublesome host may be a stop gap measure so i decided to block troublesome networks from our mail server.
Some networks are sewers and when i see vn and cn from the reporter a quick cidr check (one that china is unwilling to publish via apnic and a compute with some perl) and ip add prohibit seems to have made life easy from compromised computers.
The countries vary for instance Bahrain is currently hot, and Vietnam not so with the probers. China remains a consistent sewer. North Korea (my blog) is unheard of although the odd single South Korean ip address occasionally appears so no they did not hack sony.
If the traffic is dumb then i have no problems with the idea of nobody home (my blog that is until the next reboot) which is about once a month.
So watch out for apes with mallets who might make you think the internet is broken