We have had this very same thing occur, XXX spammy links, among many others attacks.
We found this was a competitor wanting our market share. They hired kiddy scripters to do the dirty deed of the spammy links which apparently is easy to find people who are always trying to hack XXX sites. The end results is to ruin your Google backlinking ratings, i.e. in general hurt your overall Goolgle authority and rankings.
The secondary result it ties up your time and takes you away from running your business which also is to their advantage.
The sad part is that there is no way to protect your self from these low life tactics.
Unfortunately, we expeirenced simultaniously robo call attacks taking down our phone systems and over filing our voice mail and at the same time, had every email account know to the general public submitted to spammers to fil up our servers and mail boxes. Definetly a planned set of events.
They topped it off with constant DDOS attacks, and attempted SQL injections and any other thing they could think of. Of course this makes the customers unsure if were still in business because the site was up and down and of course they wondered if it was even safe to shop. This has gone on for 3 years, until we finally found a safe hosting arrangement, 12 moves later and have extra phone and email security measures in place. We are still fighting to get back in Google's good graces.
Again all taking time away from running your buisness.
So a few spammy links to keep up with disavowing, no problem. Count your blessings. (-:
