Checking some logs I realized that comment spam was originating from a host in Japan at: 2001:2e8:626:0:2:1:0:b7.
With the plethora of IPv6 addresses, it will only be a matter of time before we see massive comment/email/and web spam originating from IPv6 address blocks.
And what exactly is this machine that is sending comment spam?
Why, it’s a default install of Centos with a bunch of open ports. I am sure some not-so-friendly scripts have found their way inside this vulnerable host and have started using it to generate spam. The fact that the machine was IPv6 connected was likely a coincident, but a useful one (to the spammer).
I have now blocked the /64 of that range to prevent such annoyances.