I've seen spam on sites with far less traffic than chess.com
Targeted by Pro-Spammers. Quite a Honor, is it not?
Sort:
To this extent?
Because this is a soft target
Get a life, Daddy-O 
This website seems to have been the target of organized and professional "spammers" for the last several months. Obviously pro spammers aren't going to waste their time hitting a site with little traffic, so the targeting of Chess.com is something of a sign that this site has "made it in the big leagues" so to speak.
You yourself may be a regular user of websites and forums with many more members and traffic than this one. Do you notice this level of "spam" on those? If not, why on this site and not on other sites with much more traffic and members?