Online business as Craigslist continues to ban sites IP from Nigeria

I was quite dumbfounded to see that I couldn’t enter my Craigslist account today, Aug. 14, 2015. I got an error like the following:

This IP has been automatically blocked.
If you have questions, please email: blocks-b13577657272204@craigslist.org

I wondered what that meant.

I know as well that many 419ers in Nigeria who specialize in online marketing use Craigslist as the main domain where they transact their business, but I'm wondering why ban multiple IPs from that country?