We here at Defensio HQ see a lot of spam; spam in all its flavors and incarnations. Occasionally we see new techniques that baffle the mind. URL-less spam (that is, spam not containing URLs) is one of these baffling new forms of spam we've seen cross our desk, so puzzling that it's worth delving in to try to understand what in the world it means.
URL-less spam looks like the following:
Notice that this commenter (i.e. spammer) has not left a URL with his/her credentials, nor has he/she supplied any URLs in the body of the comment.
Why is this strange? Because the entire reason spammers typically hit blogs with their bogus comments is to populate the web with URLs that link back to their spammy sites, and thus manage to exploit the Google juice of the sites they breach with the goal of boosting their own search engine rank. And so, bombarding a blog with comments that do not contain URLs defeats the whole purpose, and results in no obvious net benefit to the spammer, other than the evil satisfaction of annoying the hell out of bloggers.
So if not to exploit Google juice, why do spammers go with a URL-less approach? Two theories:
1) To "train" spam filters to allow specific keywords.
Filters that use statistical filtering learn over time. By having legitimate-looking comments make it through the filter, while containing a handful of specifically-chosen keywords, spammers could be trying to tip statistical filters toward starting to consider such keywords as innocent, thus increasing the likelihood that future spam comments containing these words will bypass spam defenses.
2) To be whitelisted.
Some spam filters allow users that successfully post comments X number of times to be added to a whitelist, meaning they will bypass the filter in the future. Since URL-less spam typically looks fairly normal, spammers hope that bloggers will fail to identify their comment as spam enough times that auto-whitelisting might kick in.
These motives are simply our best guesses at what might be in spammers' nefarious minds. Who knows, simple annoyance could be their sole, inexplicable, goal?