Except that nefarious is not a direct synonym for criminal. Nefarious has a subtext of specific underhanded malicious intent, whereas criminal doesn't have the same intentional connotations.

If one were to read about a "Criminal website", it might have instructions on how to make a bomb or something like that, whereas a "nefarious website" is likely to be read as looking normal but stealing your information.

By calling the sorting nefarious, OP has (likely) unintentionally implied that there is an underlying sinister reason for the issues, which is not likely to be the case.

I guess I'd want to know if I was using a word incorrectly. I understand what they're trying to say, but nefarious doesn't make sense in this context. Maybe my pedantic correction prevents them from looking dumb in the future.

Because words have meanings? If words just mean anything you want them to mean then they mean nothing.

I’m thinking you could care less.